I love Playa but it may not fit your wish list for snorkeling from shore. There is no reasonable snorkeling off Playa without a boat ride. I have swum out to the reefs near where the boats dock, i think by 28th street, but it is a long and dangerous swim due to boat traffic and possibly current. I went out a few times with a few local spearos and spent probably a half hour swimming out. Puerto Morelos has great snorkeling by boat, and some shore snorkeling with only a bit of a swim. Akumal is probably the best bet if you want to be able to walk from the hotel to the beach and snorkel out to the fringing reef. Great number of sea turtles, decent reefs and generally a really chill place. Do not need a boat, no need to pay for a tour and especially in the mornings will have the ocean mostly to yourself. Only caveat is that there is damn near nothing to do outside the resort without taking a taxi or collectivo into Playa or Tulum town in my experience. So for me it would be 1 of 3 choices in that area, in order I'd pick them.
1. Stay in Playa- plenty to do for kids and you, easy to self cater, catch a taxi or collectivo with the family to Akumal or Puerto Morelos and spend the day on the beach/snorkeling (get drinks and snacks at Oxxo by entrance to Akumal or bring your own, few average restaurants on beach, catch bus or taxi back. But if bad weather or don't feel like snorkeling, plenty to do.
2.Stay at Akumal- instant access to reef and beach, snorkel before the crowds and after in evening. need to take taxi into PDC or Tulum for any kind of evening activity. From what I know, fewer lodging choices and more expensive than Playa.
3. Puerto Morelos- reasonable lodging cost, decent amount of restaurants, not much nightlife, can snorkel from shore or by boat, better than playa snorkeling, I would say slightly less impressive than Akumal, but youtube videos and decide for yourself
FWIW personally I would avoid the "adventure parks" like the plague. they are sterile, disneyland type theme parks that cost an arm and a leg, especially for the whole family. I know many people do like them but for me I would avoid. Xel-ha is the only one that feels even a little "natural" and the vis and wildlife can be terrible, especially once the crowds show up. Aktun Chen is the only inland "adventure park" I would even hesitantly recommend, it at least felt locally run and the cave was impressive, plus you only pay for the activities you want. Sorry not familiar with Cabo or Puerto Vallarta.
I am biased to PDC since it is such a central location, no rental car needed, can spend as much or as little as you want and great mix of taco stands or amazing Italian restaurants, coffee shops and nightlife, cenotes and ruins, something for any mood.
