Reading a bit more into the financial side of things — PayPal users must be 18 or must be using their parent's account. Adults can have one personal and one business account, so that wouldn't really work. It also isn't easy to get a plastic PayPal card.
I hadn't thought about the minor accounts which obviously complicates things. It would have been harder to pitch but easier to start with small payments between friends in the app and work back around to the chores/PiggyBank idea.
Still seems reasonable to expect a parent to set up a bank account for their child and then facilitate PayPal deposits into an account. ACH deposits have low fees but they're delayed one or two days. Was instant gratification the blocking factor? Why not use Bitcoin, for the hell of it.
So I don't see what the problem is with — supply your own debit card, child's bank account, and adult PayPal account — then sign-up and press on.