First, modules:

• Views + CTools
• Entity Views Attachments
• Entity Reference 7.x-1.0-rc1
• Entity reference prepopulate 7.x-1.0
• References dialog 7.x-1.0-alpha3

Then, content types and fields:

• Create four or more content types. For this example, I will use Client, Work, Task, and Note. Tasks and Notes can be 'attached to', e.g. entity reference, Client and Work nodes. Also, Work nodes can be attached to Clients. In my use case, I have several other content types, which can 'have' Tasks and Notes as well. The other content types in my use case also have entity references to Client and Work nodes.
• Client is the ultimate parent content type, so you don't need any entity reference fields on it (unless you want them for some other purpose, of course).
• On the Work content type, create an Entity Reference field using the autocomplete widget, called 'Client'. You can make it required if you want, but it does not have to be.
• Check the "Enable Entity reference prepopulate" box, select "Disable field" for Action and "Do nothing" for Fallback behaviour. I usually set Skip access permission to "Administer site configuration".
• If you want to enable the References Dialog widget to be able to add/edit a Client from the node add page for a Work, check the Edit and Add dialog boxes

• In the 'Client' field settings, leave the Number of values at 1, Target type is "Node", and select "Client" for the Target bundles

• Now, on the node add page for the Work content type, you will see the Client Entity Reference Field, with the Add Client link supplied by the References Dialog module:

• Then, on your Task and Note content types, create (separate) Entity Reference fields called 'Attached to' (machine names: field_task_attachedto and field_note_attachedto), that can reference an unlimited number of Client, Work, and whatever other content types that you desire. You should use different fields for ease of management, but the settings are the same.
• Check the "Enable Entity reference prepopulate" box, select "Disable field" for Action and "Do nothing" for Fallback behaviour. Set Skip access permission to "Administer site configuration".
• You will not be able to use the References Dialog links since you are enabling the field to reference an unlimited number of different content types. With child content like "notes" and "tasks", you presumably are not going to be creating a parent, like a "client", when you are creating a "note" for the "client" - the "client" parent node will already exist.

• In the Attached to field settings, select "Unlimited" for the Number of values, set the Target type to "Node", and select the Client, Work and any other content types to which you want to be able to attached Notes and Tasks under Target bundles.

• Remember to create your "Attached to" Entity Reference field on both your Note and Task content types. If you recycle the field, it will have the same settings for both Notes and Tasks, so if you want to be able to attach Notes, but not Tasks, to some content types, then use two separate fields with the same settings.
• First, create your Views to display the Notes and Tasks attached to a referencable node being viewed. I also have pages to display all of the Notes and Tasks, but I want to be able to see all of the Notes and Tasks attached to a Client or Work on the Client and Work nodes. Here, Entity Views Attachments (which is a great and useful module) comes into play. I'll use the example of Tasks again, but the process is basically the same for Notes - just change anything that was specific to Tasks to Notes when creating that View.
• At admin/structure/views, click the "Add new view" link, name it something like "Attached Tasks" and select Show Content of type Task. Uncheck create a page, and leave create a block unchecked.
• Use the "+Add" button near the top, to add an "Entity content" display to your newly created View
• Under the "Entity Content Settings" pane, select "Node" for the "Entity type", and select the content types that can be referenced by the "Attached to" Entity Reference field on the Task content type (e.g., Client, Work, etc.). Leave Arguments at id. I opted to display the title of the View display by selecting "Yes" for Show title.
• Add the fields that you want to display. Title is fine for now.
• Then create your contextual filter, so that this Entity Views Attachment display only shows on content types referencable by the Attached to field on the Task content type, and to show only the Tasks that are attached to the node being viewed.
• Expand the "Advanced" pane, and click the "add" button next to Contextual Filters to add your new Contextual Filter.
• Select the "Attached to" field (machine name: field_task_attachedto), which will be listed as "Content: Attached to (field_task_attachedto)" to use as the Contextual Filter.
• Under When the Filter in Not Available, select the "Provide default value" radio button, and then select "Content ID from URL".
• Under When the Filter Value is Available or a Default is Provided, check the "Specify validation criteria" radio button, select "Content" for the Validator, and then select all of the content types that can be referenced by the Attached to field on Tasks (Client, Work, etc.). 
• Leave the select list option for Action to take if filter value does not validate to "Hide view", which is the default and the desired behavior.
• Click the apply button to save the new contextual filter that makes the magic happen!

Basic Entity Content View Display set-up:

Configuration for Contextual Filter on Content: Attached to (field_task_attachedto):

• Now, after saving your new View, you will see Tasks listed on the nodes that are "attached to"/referenced by Tasks. Note, there is currently a bug in Entity Views Attachment that does not automatically make the Entity Content display available on content types. First go to the "Manage fields" tab for the content types, and then go to the "Manage display" tab. You should now see the Entity Content display field for the View you created, and you can position it where you would like in relation to any other fields. Here is a shot of what a Client node should look like, after you have created the Client and an attached Task:

• Repeat the basic process of creating the EVA View to display Tasks attached to a node for the Note and Work content types. You can also display the View in a block instead of an EVA, which will allow you to display the child content type attached to a node in the sidebar or other regions of your theme.
• Next, create the Views to be able to display "Add new [child_content_type]" links on parent nodes. Like with displaying the child content on parent nodes, you can use an EVA or a block to display the "Add new [child_content_type]" links on the parent nodes. This example will use creating the link in an EVA for the Tasks content type, but the basic process can be repeated for Notes, Works, or any other child content types - just make sure to use the correct fields and filters applicable to the work. Finally, Entity Reference Prepopulate comes into play:
  • At admin/structure/views, click the "Add new view" link, name it something like "Add new child links" and select Show Content of type All. Uncheck create a page, and leave create a block unchecked.
  • Use the "+Add" button near the top, to add an "Entity content" display to your newly created View
  • Under the "Entity Content Settings" pane, select "Node" for the "Entity type", and select the content types that can be referenced by the "Attached to" Entity Reference field on the Task content type (e.g., Client, Work, etc.). Leave Arguments at id. I opted to not display the title of the View display by leaving "No" set for Show title.
  • Add the "Content: Nid" field to your View, and remove the Title field.
  • For your filters, set the "Content: Type" filter to show only the content types that can be referenced by your "Attached to" field on the Tasks content type.
  • Change the page options so that you only display one piece of content (which will happen automatically once you set the contextual filter for this view).
• Now, you need to set up your contextual filter on this display so that it is used only in the context of a node which can be referenced by your "Attached to" field on the Tasks content type.
  • Expand the "Advanced" pane, and click the "add" button next to Contextual Filters to add your new Contextual Filter.
  • Select "Content: Nid", listed as "Content: Nid" to use as the Contextual Filter.
  • Under When the Filter in Not Available, select the "Provide default value" radio button, and then select "Content ID from URL".
  • Under When the Filter Value is Available or a Default is Provided, check the "Specify validation criteria" radio button, select "Content" for the Validator, and then select all of the content types that can be referenced by the Attached to field on Tasks (Client, Work, etc.). 
  • Leave the select list option for Action to take if filter value does not validate to "Hide view", which is the default and the desired behavior.
  • Click the apply button to save the new contextual filter, and then save your view.

Basic Entity Content Views Display set-up:

Contextual filter configuration:

• The final step on this View to make it usable is to rewrite your NID field so that it is output as a link on a parent node to add a new Task node with its "Attached to" field properly referencing the parent.
• Click on the "Content: Nid" field, and uncheck the "Create a label" box
• Expand the "Rewrite Results" section, and check the "Rewrite the output of this field" box
• In the Text box, enter <ul><li><a href="/node/add/task?field_task_attachedto=[nid]">Add new Task</a></li></ul>
• In the node/add/task part of the above, 'task' is the machine name of the child content type Task, and field_task_attachedto is the Entity Reference field on the child content type that can reference the parent node being viewed. Basically, with Entity Reference Prepopulate, the above link tells Drupal to go to the create new node page for a Task with the "Attached to" field pointing to the parent node being viewed. For the Notes content type and its "Attached to" field, the rewritten link will look like <ul><li><a href="/node/add/note?field_note_attachedto=[nid]">Add new Note</a></li></ul>

Now, when viewing a parent content type like a Client, you will see the Tasks attached to that client, and a link to add a new Task node from the Client. Once the Views for the Note content type are set-up, you will see the whole deal: