My son stepped on a rusty nail and he has had his dtap series done, will he be ok?

See a doctor: Puncture wounds can be tricky and since you know it was a rusty nail, it needs to be cleaned out well and possiblhy started on antibiotics.

Your ? raises ??: As far as tetanus goes, a shot within the past 5yr gives good coverage. The injury may involve other risks. Was he walking in a stream or lake? On open ground? Through a sweaty tennis shoe ?Cleaned thoroughly with soapy water or antiseptic solution? I've seen some bad ones have to go to the or & be drained after they festered up. Monitor closely & have evaluated if pain, redness or drainage is seen.