Dunno how much I'd trust consumer grade biometrics. When your kid hits oh... about 7-8, they'll have a harder time ordering up some lockpicks, or learning to crack a combo lock than they will finding access to some crazy glue, gummi bears, celophane tape, a microwave, and the internet.
With such long term intimate contact with the key (you), that above is enough to get through even some professional grade fingerprint scnanners.