Cool thing about at home conditioning is they can pace themselves. Whatever they do is a benefit. But I wouldn't expect a lot, its rec. Better they do it because they want to.
I would make sure they are exercises they can do well. Give them a start point (low reps/time) have them work up to max.
Just for something to think about. Here is the conditioning my daughter does when not in the gym (coach doesn't expect them to do it on gym days). Again just for ideas I wouldn't necessarily think a rec kid would be doing all this. The other thing is when they start to see results (as in their gymnastics gets better, hopefully, its its own incentive, but again it really depends on the kid).
Cardio: Run / swim or bike 20’
Stretching (team warm up)
Squat straight jumps 20x
Wall sit 1min
Wall handstand hold 1min
Leg kicks 15x each
Leg pulses 10x each
Press handstands 10x
Push ups 2x20
Plank 1min all sides
Mountain climbers 20x each
1 leg squat 10x each
Releves (use weights) 50x
Chin ups 4x5
Hollow hold 1min
Arch hold 1min
100 abs, sides, back
Arms only arch ups 50x
Fire hydrants 15x each
Heel drives 50x each
Shoulder stretch 30 sec each
Half split against wall 1min each
Center split against wall 1min
Pike stretch 1min
Feet stretch with band