Tuttle twins have a great episode about bitcoin. There are also a couple books and games for kids about bitcoin. I think letting them earn some via zbd games etc is a good starting point. They get some sats and then send some sats and you explain along the way that they are using the lightning network and what the difference between base chain and layer 2 are and the difference between a custodial wallet like zbd and a self custodial wallet. Of course you do this over time.
Oh! I don't know the Tuttle twins, I'll look them up. I downloaded a couple of simple games for him, and he says: "Mom, lend me your phone to earn satoshis."
Regarding the wallets, I must explain more. Recently, she was asking me if she could buy things with the sats. We explained to her that it was possible and she was amazed.