What is the penalty for obtaining a child's passport without the consent of both parents?

It is potentially a contempt of court. I would look to your agreement/court orders regarding traveling with the minor child. If the passport was truly in violation of any existing court order then the other party is potentially in contempt. Again, however, the issue of travel is usually addressed by court order or agreement of the parties.

Massachusetts has no requirement that both parents signatures be required to obtain a passport. In my practice, I frequently add a clause to a separation agreement restricting the ability to get a passport. In the absence of such an order, there is no requirement that both parents sign to obtain a passport. You need to check with a New Hampshire attorney for New Hampshire law. As for signing a father's signature, there are laws that make forgery of documents a crime.