If they actually did provde services--e.g. redo your roof--then yes: you have to pay. That is because the law does not allow you to accept a product, service, payment, or benefit from another (in this case, a new or repaired roof) without paying for it; keeping a benefit without paying is called "unjust enrichment," and the law strongly disfavors it. However, if you did not already accept the services, you could void the contract without penalty, since you minor child may not legally enter into a contract; you would not have to go ahead and let them do the roofing work.