First, the issue is if a minor can sign a contract. Based on the video, which can be seen through the link above, JoJo signed the record contract at age twelve. The JoJo also said she felt taken advantage of. In fact she was.
A tenant of contract law is that the person signing the contract must have the legal capacity to enter into the contract. This is measured against the person being obligated to conform to the contract. As an example, a fifteen year old who is acting on behalf of a twenty year old can sign a legally binding contract because it is the twenty year old being bound by the contract. However, by definition a minor does not have the capacity to contract for themselves.
This is not absolute, contracts for food, clothing, and shelter will all be enforced. However, as a general matter, a minor is not legally bound by a contract. The minor can, by failing to act, become bound by the contract upon turning eighteen. Before this point, the minor can elect to void the contract.
This goes directly to the second point.
Second, JoJo also spoke about the need to get “lawyered up” as something she learned. This is important for two reasons in the situation described. JoJo described the contract as “legal mumbo-jumbo.” She also spoke about how difficult it was to escape the contract once she turned eighteen.
It is the job of your lawyer to educate you. The ethical rules binding attorneys demand that the client make final decisions about goals and accepting offers. A lawyer should explain the legalese so a client can make an informed decision. If you have questions ask them and if your lawyer is not answering you to your satisfaction, find a new lawyer.
Additionally, it is the job of the your attorney to find the problems and address them effectively. In this instance, if a lawyer had been retained before JoJo turned eighteen, it may have been fairly easy to void the contract.
This situation sounds a bad situation where a positive result may not have been possible. Sometimes there are no good answers and sometimes all that can be done is making the best of a bad situation.