Add that puppy's teeth are a nightmare... and I can believe you child cries
.
Ok, when he bites you, you should cry (like they do... imitate their crying), then say a kind NO and offer him something else to bite as soon as he leaves you. Be patient.
Do you know some other dog he can stay with few times a week (obviously vaccinated and equilibrated!) that can teach him how to behave?
It would help a bit.