Don't assume that a parent is the legal guardian of his/her child. Legal guardianship is a status granted by a court.
Oklahoma has two provisions of law regarding minors' accounts. In one (6 OSC 903.1), a bank may accept a deposit account from a minor if the minor is the sole and absolute owner (no joint accounts); the "disabilities of minority" are removed for the purposes of allowing the minor to enter a binding deposit contract; but the parent or legal guardian of the minor may deny him/her the authority to control the account and take the account over, requiring that any withdrawal from the account be approved by the parent or legal guardian until the minor reaches majority. That's clearly not a description of the account you're asking about.
In the other, at 6 OSC 901, a joint account is permitted, including one owned jointly with a minor, but the provision does not remove the "disabilities of minority," so banks have done various things, including side agreements in which the adult joint owner assumes legal responsibility for any transaction of the minor.
John S. Burnett
Fighting for Compliance since 1976
Bankers' Threads User #8