First, a minor should not be signing any contracts. Second, if you are looking for an entertainment attorney, you can contact the Philadelphia Bar Association - they can put you in touch with a number of skilled entertainment law practitioners in the Philadelphia area.
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As noted, a minor lacks legal capacity to sign any contract. The parent or guardian will have to sign, and the party on the other side, if eligible for court apporval, will need to get that court approval. That requirement benefits the minor, since the other party may not know this or do this.
As for getting pro bono legal help, you can try the bar association, as my colleague suggests, or maybe a local law school clinic. I know there are Volunteer Lawyers for the Arts in a gew cities but I don't think Philadelphia is one of them, and I don't think the speed and/or quality of the work provided is necessarily very good. But it's hard to find people willing to work for free, and I'm guessing you don't work for free and don't like to be asked to do so. Plan to get what you (don't) pay for. Legal services may be expensive, but good preventative legal care can truly be priceless.
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If you want a pro bono entertainment lawyer, try Volunteer Lawyers for the Arts in Philadelphia. Just be aware that you have to qualify for pro bono services. They also have people who work at reduced rates.
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