Ask yourself this question "If a minor cannot enter into a contract under WI law, how will you proceed with collection if the account becomes overdrawn?" If you have access to Brady on Bank Checks, this issue is addressed and the bank is left holding the loss. For this reason, we require a person who is over the legal age to also be on the account (owner...not just authorized signer) so that we may collect from that individual if the account goes negative. To avoid potential UDAAP violations do not require the second person to be a parent and be consistent with the second owner requirement.
Additionally, I support your idea to offer these accounts as it helps the financial literacy of our youth.