M.,
My family is also a fan of Mexico - my husband and I (and my parents, our siblings, nieces, nephews, etc.) have traveled many, many beaches in Mexico.
I have found the Destin, Florida beaches to be most like Mexico. We've also been to Panama City, FL, Ft. Lauderdale (sp?), FL, the Keys, etc. We think Destin is most family friendly. They have great places to eat, great condos in various price ranges, lots of kid friendly activity (mini golf, arcades, water park, aquarium, amusement park, etc.) There are great places for the grown-ups as well.
We stayed at Jetty East (private condos) 2 summers ago and it was great. Have fun on your family beach vacation!!