When requiring photo release waivers and medical questionnaires from parents about their kids, is there a way for these records to be linked in Realm?

These are great suggestions! A few additional things to consider...

If these are connected to an event that you could serve up in a Registration Event, ie Youth Camp/VBS, you are able to attach "Resources" to events for people to download and fill out and email or bring into the church.

You can also ask Custom Questions within the event that can be linked to update Profile Fields. You may find that you need someone to agree to a statement and can accept a simple 'Yes" only option for an agreement. Like, "Do you agree to pick your kid up by noon on Friday?" In order to complete registration, you can make that a required answer, and the only option to choose is "Yes".

There is a way to attach files on someone's profile. If you look under their profile in the line where it says info, groups, etc the last item is attachments. You could attached the waivers and questionnaires on their account. 

You can attach the signed documents to the parents' records.