Driving, particularly on the coast highway (Rt. 307) is easy enough, if you can do Boston at rush hour its no worse. There are a couple of quirks; if you want to make a left hand turn, you pull off to the right and wait for an opening, so you have to be prepared for others doing the same, sometimes across 4 lanes. Also, you should signal your intent to turn left by putting your arm out the windo.w.  Also, there are speed bumps (topes) at many lights and intersections, not always where you expect or marked.

One favorite area is Tulum. A lot of variety in hotels, from palapas with sand floors to upscale spas.  Ana y Jose's has the best pool in the area and a great beach. Their restaurant is OK, but pricey, and it gets old after a few days and the service is very slow, even for Mexico. The best rooms for families are the suites, which are on the beach; some of the other rooms are sort of dark.  Book early, they fill up. They rent cars so if you dont want to drive all the time you can get a van and driver for airport transfers and then rent a car by the day if you want to explore.

A little cheaper is Piedro Escondida a mile or two up the beach.  The food at Zamas restaurant Que Fresco is pretty good as well. The Tulum ruins are worth a couple of hours (at most with kids), but go early, and bring water, it gets hot. 

This goes double for Chichen Itza, which is a long day trip from the coast; it gets very hot and the site is huge with a lot of walking. Better would be a night at the hotel, so you break it up.  There is a funny old hotel right at the site, with a bunch of options for rooms. There are some separate cottages with two room suites that are good for families. It's not cheap but it's worth it if you want to see Chichen itza.  The hotel has its own entrance to the ruins. The ruin is huge, hot and lots of walking, kids tend to burn out pretty quick.

Punta Allen is 50 miles south of Tulum down a moderately bad road. There is not much there. The village is sort of a dump, and the beach is lousy and dirty. There's no reason to go unless you want to fish. For bonefish and maybe permit, its the best deal around.  You can get a guide with a panga for maybe $250/day and poke around the huge lagoon. There are "eco-tours" which means a guy with a panga will ride you around the lagoon and the channels for a couple of hours. Not worth 50 miles of bad road. A mangrove is a mangrove is a mangrove.

Another good day trip is the town of Akumal, but it is more "Americanized." There are lots of condo options for staying at Half Moon Bay but only a few have a pool. The beachside restaurant in the middle of the bay (La Buena Vida) has a lot of ambience and a great view but the food is average to poor and the service is very slow. There is a much better place in the village, run by an American couple, to the right of the parking lot (Hul-Ku). The lagoon at Yal Ku at the end of the Akumal Road is the best deal in Mexico.  Admission to this national park is about 6 or 8 US dollars per person.  They rent snorkels and fins and have a snack bar,  a fresh water shower and a bathroom. The fish are numerous and very tame.  It is set in a sculpture park with lots of stairs into the water and lots of picnic spots.  Bring lunch and spend a couple of hours; its easy snorkeling for kids.  The reefs in Half Moon Bay are great too, but the waves and currents are more difficult that it looks so you have to be careful. There are often turtles in the bay.

Near Tulum is Casa Cenote, a free cenote next to the beach.  Good snorkeling, but you need your own stuff. You can park at Casa Cenote, have lunch, and snorkel both in the cenote and off the beach in front of the restaurant. The cenote is easy snorkeling.

Also maybe worth a trip, although expensive for what you get, is Hidden Worlds. Some zip lines, a "sky cycle" (you pedal along a zip line in an open contraption), swimming in a cave cenote.  You ride around the jungle standing up in the back of an open truck.  Don't do it if you have a bad back or are afraid of heights.

Playa del Carmen is fun for a couple of days. The beach is OK, but crowded. There are literally dozens of boutique hotels and restaurants to choose from.  Fifth Avenue is a mile long walking street two blocks from and parallel to the water, with everything from T shirt shops to fine dining. If you want peace and quiet stay someplace off the avenue.  The action starts to peter out around 16th street, so its quieter to the north. The north end tends to be a little more upscale as well.