Password protect Android market place

Hello everyone,

I just got a new tab (Samssung Galaxy for the Win!) and I want to let my little brother use it but I'm kind of worried he might go to town on the market and buy a bunch of crap I can't afford. He's 5 and has poor impluse control (Trust me its happened before) Is there anyway I can password lock the Android store so he can use the tab with out killing my credit card?