We stayed in PV in June for 10 days about 3 years ago and found it starting to get humid. We usually did what we wanted to do in the morning, stayed by the pool in the afternoon, then went out to town in the evening when it was more comfortable. Most people probably wouldn't want to go there after the middle of June when the rainy season starts and the humidity goes way up. I guess it all depends on what you're used to and your tolerance to heat and humidity.
Most people agree that Cabo is less humid. But, the owner of the Cabo dive shop I frequent, said don't come down around September because it is miserable (hot & humid) in Cabo at that time.
I often read were people say Cancun is more weather friendly. A year ago last February we went to the Grand Mayan south of Cancun (closer to Playa del Carmen). If we were right on the coast it was extremely windy. When we went inland just a mile or so to dive a cenote, it was very hot and humid. A few people were close to passing out from the heat and everyone was being warned to stay hydrated.
I guess what I'm saying is it is hot and humid in Mexico in the summer, but you can plan your day around the weather and have a great time. I wouldn't rule-out any particular area based solely on the weather. I would place more emphasis on what activities would be available for your family to enjoy.
Marty