To be specific, the account must be opened in the minors name with a legal parent or guardian as a co-signatory.
Either way, you're right. Minors can not, in the United States, enter into a legally binding contract. They can't even legally purchase a car as there is an implied or express purchase contract.
A bank checking account has all kinds of interesting legal issues WRT bounced checks, so I couldn't open my checking account until after my 18th birthday. Also no credit cards until I was 18.
Nothing defines arbitrary and capricious like our financial and legal systems, so this could have changed last week, probably to "protect us from the terrorists" or "save the children".
Only one of my friends was allowed to use their bank account - for everyone else it was college savings only, and all spending money had to be cash.
With my parents' permission, I was able to have a debit card (which processes in the payment network like any MasterCard but has no line of credit) attached to my checking account at 17.