"Family" registration

This would be some kind of group variant where up to N people can register for one fixed fee with each additional member being an additional fee.

For example, we offer a family registration where two adults and up to 3 "youth" can register for an event at a fixed price - let's say $100. Additional "youth" are an add-on of $10 each.

Think you can do most of this already. Right hand side of the event setup there is a Rate per Person

You set this to:
1Person $100
2Person $50
3Person $33.333
4Person $25
5Person $20
6Person $18.22
7Person $17.14

You can control the adults and children bit this way...

Why thank you! I'm still new with the product. I've seen the per person but it didn't occur to me to split it up that way.
We're a small enough organization that we pretty much trust people with the adults and children thing.