No, advanced cert is not required. The DM for whichever dive op you choose should start you out slow and check out your abilities and move on to more challenging dives as they get used to your skill set. As you see from my original post here, my wife and I used Blue XTSea while staying there at Casa Mexicana and highly recommend them. All of my diving there has been with Pedro and he is wonderful to dive with. As I posted earlier in another thread, he has an easy going way of making the already great diving even better.
Walk out the door of the hotel turn right and walk to the corner, turn right again and walk less than one block to the shop on the right side of the street. Or stay straight along the waterfront for about a block and a half and there's your pier on the left. Aqua Safari is the shop closest to Casa Mexicana and their pier is right across the street but I've never dived with them so have no comment. Aldora is pretty much across the street from Blue XTSea and they use the same pier. You can't go wrong with them either as we've used them before too and were most satisfied.
I'd contact them both, tell them your experience levels and what your ideas for the trip are and then see which one best suits your needs while there. I think you and your son are in for a treat. Have a good trip!