My husband and I took our two kids (3 and 1) to the Sandos last week, and it was a great experience. We booked the hotel solely based on reviews and the kids' waterpark, and it did not disappoint.
Check-in and rooms: The transfer from Cancun airport is relatively quick (45 minutes), and the check-in process was seamless. We arrived around 1 pm, so our room was not ready, but we were told to check back at 2 pm (it was ready then). Rooms were clean, a decent size, and had a king bed and a bunk bed. My booking papers said we had an eco family superior room with a trundle bed, but I was later told those rooms don't exist, which was disappointing, as I was hoping to have my 1-year-old sleep there (she ended up in our bed, which was not ideal). I have no complaints about the rooms, apart from the fact that the storage isn't terrific for a family of 4 if you don't want to live out of your suitcase. The location we had was terrific. It was just on the other side of the lobby cenote. A bit of a walk from the beach and main pool, but super close to the kids' aquapark.
Restaurants: The main buffet restaurant was closed for renos during our stay, so we had the option of going to the Italian or Mexican buffets. I personally don't think the food was terrific (I have had better at other hotels in Mexico), but they offered a good selection of choices for adults and kids at every meal. We often went to the Mexican because it had more options that my kids liked. Service at both restaurants was always excellent, though we usually went at times when it wasn't super busy (10am seemed to be insane for breakfast). We also tried the Tapenyaki restaurant. We couldn't get a reservation ahead of time, but walked up at 6 pm and were able to get a table. My 3-year-old LOVED the experience, and the food was great, so I highly recommend.
Pool/beach: The beach is really lovely apart from all the sargassum in the water. If you don't care about seaweed, it's a great spot to be. We split our time between the kids' waterpark and the main pool, both of which are great. The main pool on the side with the bar was pretty packed by the end of our stay, but we were always able to get chairs regardless of what time we went. One thing to note about the waterpark - it's closed on Tuesdays for maintenance, and the large slides also do not accommodate adults AND kids. There are some for kids only and some for adults only, which was disappointing for my son, who was too nervous to go down the kids' ones alone and couldn't go down the adult ones with my husband.
Gym: I took advantage of the on-site gym and went every day. It's clean and has a decent selection of equipment (treadmills, an elliptical, and machines). There are free weights, but only one of each up to 45 lbs, I think, so if someone is using the one you need, you're out of luck. It opens at 7 am, which was later than I expected, but it worked.
Grounds: The hotel grounds are beautiful and a really great place for kids looking to explore nature. My son always wanted to "walk through the jungle," and he saw coatis, iguanas, lizards, and monkeys pretty much every day. The cenotes are beautiful, but you couldn't swim in them while we were there. For anyone booking with small kids, there is a LOT of walking, so a stroller is a must. The other thing that I loved/hated was the animal keepers' area. It's great for kids to be able to pet farm animals (sheep, pigs, bunnies, chickens), and the enclosures are really well kept, but I question their quality of life and honestly feel really bad for them. The pigs are kept on concrete floors, and the sheep are on sand with really nothing to do; they kind of just lie in the corner all day; kind of sad to see.
As a side note, be prepared to pay $$$$$ if you want to buy anything from the stores. I got burnt and needed some hydrocortisone, and what she offered me was $55 USD (I am Canadian, so I think that was roughly $80)! We ended up taking a taxi to Playa, and I got some at a pharmacy for 300 pesos. I also saw a sign for 2 bags of chips for $20 USD, which is outrageous. If you need to buy anything and don't want to spend all your money, definitely head into downtown Playa instead.
Overall, it was a great trip that my kids loved (it was their first time on a plane and in Mexico), and I would definitely recommend it for families looking for a unique and exciting resort with lots of activities for kids. Its proximity to downtown Playa is also great, especially if you need to pop into town for anything.