I think our account number was 14? Simple enough for a child to remember.
Around age 9 I was using the account on my own to buy food after school. I'd state the account number, and the cashier would write the credit down with a pen into a special notepad they kept under the cash register.
A recent observation:
Shop to a little girl: What's your Numbra?
Little Girl: 718-.....
Owner comes by: That's Sharon and Jacob's account. You are not his daughter.
Little girls freezes.
Owner continues: Unless you are their niece from Upstate who has come for Christmas.
Little girl visibly relaxes and the grocer bags her items.
With contactless today I guess you can solve it with just one person, but I really liked the two-factor.
And the community service, of course.