Hi @jaredagia! As you are new to the community, when you get a chance, please introduce yourself here.
ODK-X does not have repeat groups (ODK does) but as you note there are linked tables. If you don’t want to use linked tables, you can program questions in repeatedly and then use skips, but I would really recommend using linked tables – that’s what they are designed for, to capture different levels of data (e.g. children under 5 years in your case).
You can constrain the number of responses (instances) in the linked table to be the right number of children, that’s what I usually do for surveys, although there may also be some way of creating the right number of instances too if you are more programming savvy than I am 