Funny — I’m researching the same thing. I have 15 mo. old twin toddlers and the ones we are considering are:
Club Med Ixtapa
Crown Paradise Club in Cancun
Paradisus in the Mayan Riviera (south of Cancun)
Melia Puerto Vallarta
All of these have onsite day care which is a MUST for parents of toddlers who are looking to take an actual vacation.
Hope this helps!