Concatenate text from child entity

Summary

How do I concatenate text from a child into a parent's text field?

Content

Hello,

I have a situation where data are being gathered at a child level that the user wants pulled together into a single comment text field at the parent level.  For example, instead of creating a child entity to record the child's favorite toy.  The user wants a comment text field that would list each child's name and his or her favorite toy to store in the parent entity in OSvC. OPA is creating a text value for each instance of the child that states the child's name and favorite toy. What I can't figure out is how to get OPA