If you are going to Playa del Carmen with small children, Playacar 1 is the place to be.
This villa has everything you will need and more to enjoy your vacation, 2 big bedroom with comfortable beds (if you like firm beds, these mattresses are heaven!), AC in each room and main living area, and a cool refreshing pool right there. The villa is located only 100 steps from the sand, and about 5/10 min walk to town. You might opt to rent or not a car but it is not necessary. Most of the stuff you want is within walking distance, and if you want to explore further take a cheap taxi ride or ADO buses. The beaches here are perfect, not crowded at all (like hotel beaches where you are rubbing elbows while sunbathing!).
The villa is surrounding by mature jungle like trees, which is beautiful, but be aware there are several creatures that will visit your patio every morning (raccoon like animals, squirrels, iguana, geckos, etc). they are friendly and they are more scared from... Plus