The pier here is extremely looong. There is a free shuttle from the duty free shops to the actual town. You will need to take it. The shuttle drops you off near a market with various goods. From the market it is a very short walk, (past street vendors) to the beach. At times, the water is nice, but at others it seems a bit dirty. the beach itself is alright and there are restaurants near or on the beach.
Remember that this is primarily a fishing village turned cruise port. It is not known for exotic beaches. You should enjoy it and I would feel safe with children there.I hope this did not seem gloomy, because it is nice it is just not the best beach on your cruise. You can also travel by cab, bus or rental car to Merida, which is a fascinating city near by.