Guadalajara - if you like a city....it's beautiful Colonial style old town, walking the streets, markets and vusiting the museums. Great food and reasonable in every aspect....

My favorite family travel destination in Mexico was Puerto Vallarta. The resorts are very self-contained with great pools and the town felt less touristy than Cancun, Riviera Maya, or Cozumel. The resort setup a really fun zip-lining tour with Vallarta Adventures which had great guides and was very safe (double lines for safety everywhere). We also did a day trip to Sayulita which has a gentle surf break for bigger kids (and dads).

Here's a link to Away.com's Family Vacation Guide for Mexico: http://vacation.away.com/mexico/travel-v1-cid64-mexico-cid350262-family-vacations.html. Loads of great choices here, from coast to coast!