You can't over complicate it at that age. The idea is that you set it up and they don't have to deal with balancing channels, which is complex for most adults already
Here few suggestions:
"Self custody" (no node control):
1. Pure Bitcoin
Phoenix or Misty Beez
2. Hybrid with USDT
Aqua Wallet
3. Minibits (ecash) you will save tons in fees and they get as well their personal address for a cheap price if you want to make your life easier.
Non Custodial (considering the use, is not a bad choice for now):
1. Wallet of Satoshi