It's very easy to get around, it's a long beach but it also has a paved walkway to get from one place to another and also to the restaurant. There is no need for trams or anything such as that - this isn't a "park" in the sence that it's an amusement part. The beach is very, very long so if you wanted to walk a beach, this is the place to do it. But everything to do, showers, locker rooms, the lagoon, etc. is all within close distance. For toddlers, kids this is the best beach because they have made a man-made rocked off area with the beach that is a great way to introduce children to the beach water - the hard waves (not that they are that big) do not come into this area and you could let your kids play without fear that they would be pulled out by an undertow, etc. It's a fablous park and wouldn't go to Cozumel without going there. Totally worth the $10 admittance fee.
As far as wheelchair access, if you want to go to a beach this is going to be your best best (since they do have a paved area). Anywhere in Mexico is going to be difficult because of the sidewalks not be great, etc. They don't have the requirements like we do.
As far as toddlers, tons to do here because there is a sea lion show ($5-6 bucks a person), a wild-life area which is where they keep the dolpins that swim with people, and you can walk out on the pier and see the dolphins up close. There is a shopping area and a gift shop which tons of dolphin videos, etc. Plus they have the showers and changing rooms so if the toddler gets all sandy (which they will at the beach) you can rinse off with fresh water before heading anywhere.
We always pack a small collapsable cooler from home, fill it with sandwiches and stuff from room service from the boat and take our own food - this way you're not worried about Mexican germs, etc. Not that I'm too concerned but you know what they say about the water. We even take sippy bottles and fill with juices and water from the boat so we don't have to buy any food or drinks.
Have a great time.