I got married in Playa del Carmen four years ago. It depends what you want out of the vacation. If you want to primarily dive, I would go to Cozumel. If you want to be in a beautiful town and walk to restaurants and drive to the jungle, ruins and cenotes, I'd go to Playa del Carmen. You can get to Playa del Carmen via Cancun and then an hour or so drive or from Cozumel and then a boat ride. I believe this area is safe, but if you are a little worried, flying to Cozumel and then the boat may be the safest just because you will avoid Cancun (but again, check advisories and ask around as there may be no issue whatsoever and I don't want this post to raise any red flags). If you stay on the north side of Playa del Carmen, you will get resorts that are still in walking distance to town. In the center of town there will be resorts and the beaches will be more crowded. At the south end of town is where the party bars and ferry dock is located (I'd avoid that area just for noise with a family). Just south of town, still within walking distance, is Playacar. This is an upscale residential area where there are lots of vacation rentals. We rented a place here with our friends the week before our wedding (vrbo.com) and then moved to the resort where the wedding was being held (Las Palapas). The vacation rental was very affordable and gave us a kitchen, pool, living room area. Our wedding coordinator was incredible, her name is Manuela Ek de Novak ____@____.com.
There are some water parks around there geared toward families. Tulum is spectacular and you can swim on the beach there. We had a three month old, one, two and four year old at our wedding. They went to all of these places and had a great time. Best of luck. Wish I was headed there myself.