My 16 yr old worked for first time in 2018. We've only received 1 of 2 W2's but I anticipate his total wages will be less than $8,500. Do I report or does he or both?

He files his own taxes.  A parent never reports a dependent's earned income on their own return.  If these really are W-2s and not 1099-MISC forms reporting his income, her does not make enough to have to file, but he can do so if he wants to get back any tax withheld.  He just has to make sure he says he's being claimed as a dependent on someone else's return.