After some research it looks like associated external content types can be crawled and indexed for search purposes. However I'm not able to find much documentation on querying the individual properties of the associated "child" type. Is it possible to query based on the child properties and return the source or parent info?  

Hi,

From your description, you might need the references below:

https://msdn.microsoft.com/en-us/library/office/gg294164.aspx

https://msdn.microsoft.com/en-us/library/office/ff394528(v=office.14).aspx

http://www.c-sharpcorner.com/UploadFile/anavijai/how-to-search-the-data-from-the-associated-external-content-type-in-sharepoint-2010/

Regards,