Welcome to the ODK forum, @ndalbe79! We're glad you're here. When you get a chance, please introduce yourself on this forum thread. I'd also encourage you to add a picture as your avatar because it helps build community!
The column for the repeat group in your main household information data table will have a unique value in it for each row/submission. The secondary table of children information will have a column that will have one of the unique values. If a single household has multiple repeats/children, there will be a separate row in your secondary table for each repeat/child.