First, I think having your child do the reloading, at least for practice ammo, is a great idea. By the time I was 15 I was loading almost everything I shot, mostly due to cost and availability. Stress the responsibility of loading correctly as “you will be shooting it.”
Second, For a person new to reloading I say you need a MEC single stage press. They are inexpensive and well built, but more importantly they are simple. I’ve been loading a long time -36 years- and recently got my first progressive shotgun loader. There is a learning curve with one! Especially if something gets out of alignment or adjustment.
Third, find a mentor to teach the system or rhythm of reloading. It takes 6 cycles of the press to load a round on a single stage, and that is 6 places to stop and look to be sure things are right. There is no such option on my 9000’s.
Fourth, Pick a load and stay with that until you are experienced and know how to adjust things. If you only buy and stock one powder, wad, primer, then you can’t mix it up. Sticking with one hull, I’d suggest a premium one as they load easier and last longer, and one wad and shot weight means few if any adjustments to the crimping process after you get it set up (see mentor above.)
Lastly, there will be failures. The critical thing is they never include a double charge! Messy crimps, spilled shot or powder are easy to remedy.
Even if you only break even your child now has time invested and and should be on their way to a lifelong hobby that can save money and ensure they can shoot no matter how bad the ammo hoarders get.