It's certainly possible, but I need to understand your situation a little better.
- Does the child table have a column that has the IDs of the corresponding parent table row?
- Does your InfoPath form have the owner ID already?
If the answer to questions 1 and 2 is "yes", then you only need to query the child table in the first place.
If the answer to 1 is "yes" and 2 is "no" (e.g., you have some other information about the owner table), then you can do one of two things:
1. Query the owner table to get the ID, and then perform a second query with that ID to get the child table data.
2. Create a view to join the two tables (I mentioned this in my previous post), and then query that.
Please give me a bit more detail so that I can give you a bit more detail.