take8easy....been to Mexico many times. I may be making a couple of assumptions, but are you looking for all-Inclusive type resorts/areas? There are pro's and con's to most vacation destinations in Mexico, depending on what you're looking for...As an example, if you're looking for more authentic Mexico, look at going farther south on the Pacific side....Maybe Ixtapa or Manzanillo. The issue here is the farther south or east you go, the longer the travel time and if you're going for only a week, you're giving up a day travelling back and forth.
We like San Jose Del Cabo, due to short travel time (been in SJDC in a little under 4 hr. out of Vancouver) and weather. However, due to the American Influence, this area is less authentic Mexico. Cabo San Lucus is a party destination, whereas SJDC tends to be a little quieter if you are travelling with a family. Another benefit is SJDC is only 10-15 minutes from the Airport.
Looking at the east coast, Cancun proper is a modern city, and again, less authentic Mexico. Also, Cancun is a spring break destination for University / College kids and it can get fairly crazy there in March. Riviera Maya, south of Cancun has great beaches and many fabulous resorts...if your budgets not an issue. Also, the farther south you go (South of Playa Del Carmen), maybe Tulum, the more you get into the Mayan ruins and culture. If you're into scuba diving or snorkeling, then maybe Cozumel should be your destination.
On balance, I'd suggest Puerto Vallarta. It has a little bit of everything. Plus, if you get an early flight time, you could be in your resort by mid-afternoon, same day. I'd suggest any resort along Riviera Nayarit (about 20 minute north of the airport). Try looking at Tripadvisor for user feedback on the various resorts. Many of the resorts cater to families and have Kids Clubs where you can drop-off you kids in the morning and pick them up in the later afternoon. Your kids supervised all day and most have planned activities. I know a few resorts have mini-water parks for the kids.... I know my grandkids keep asking me when we're going back to Mexico..they had a blast! If you're on a budget, look at the Royal Decameron in Bucerias SIC (about 20-25 minutes north of the Airport. The rooms are fairly basic, but again it has a little bit of everything (adult pools/family pools, activities, etc.) and the evening entertainment is family orientated.
To close, do your research, and being March, watch out for the spring breakers!