For a passport a person under 18 needs a parent to come with but my question is if the parent lost his wallet and his id was in it what else could the parent bring to show that he is who he says he is?

These are the only acceptable forms of identification:

Previously issued, undamaged U.S. passport
Naturalization Certificate
Valid Driver's License
Current Government ID (city, state or federal)
Current Military ID (military and dependents)