Final answer:
The nurse should give the second DTaP vaccination.
Step-by-step explanation:
The most appropriate action for the nurse to take in this case is to give the second DTaP vaccination. The CDC recommends that children receive doses of the DTaP vaccine at 2, 4, 6, and 15-18 months of age. Since the client has already received the first DTaP at two months of age, it is appropriate to administer the second dose at the 6-month well child check-up.