A minor cannot be held to a contract. A parent signature does not protect you on NDA either as such a promise is personal in the law. You might have a damage claim against the parents, but so what? You are still out because of the NDA violation.
Don't do the deal with a minor. The minor will win and you will lose if the minor bolts and takes the confidential information.
I agree with my colleague, a contract signed by a minor can be voided, and having the parent "co-sign" is unlikely to achieve your goal - since your primary concern is protecting the confidentiality and/or proprietary nature of the intellectual property. However, there are different standards relating to "publicly disclosed" depending on the type of intellectual property and what type of confidentiality you seek. So, it may be possible to construct an agreement that may work for your circumstances. I suggest you consult with a local lawyer.
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This answer is for informational purposes only and is not intended to be legal advice nor does it establish an attorney-client relationship. Please consult a local business lawyer to obtain legal advice that is tailored to your circumstances and facts. Good luck to you.