You can use these money to buy anything for this kid.
But you can't use this account for youself(like buy car or house). Since the money has been given to kid as a gift. There is a maximum limit per kid per year($10,000?). Please check following website.
http://www.fairmark.com/custacct/ or google"UGMA".
Of course, ther is a loophole here for IRS. A lot of people use this loophole to save TAX.