What are the best Bitcoin "piggybank" options for children? I have three children age 4-7 and I want something where they have the ability to save in Bitcoin, see their stack grow, and then spend it as appropriate. Or maybe even borrow against it at some point. Having interoperability with the fiat system is still important so they can realize some sense of converting fiat into Bitcoin, and see how the value of Bitcoin goes up in fiat terms. I'd prefer a subaccount on my account so that I don't need to use separate logins for each one. Maybe nostr:nprofile1qy2hwumn8ghj7etyv4hzumn0wd68ytnvv9hxgqgdwaehxw309ahx7uewd3hkcqpqex7mdykw786qxvmtuls208uyxmn0hse95rfwsarvfde5yg6wy7jqjrm2qp has something in the works?