Our youngest was six at the time. We did:

Cabo — 2-3 hrs whale watching (lots of options) out to the arch formation

Mazatlan — took a taxi + water taxi over to hang out at the beach, Playa de las Piedras

PV — city tour to hit a museum/cathedral or two with a little bit of beach time


Each of these had some time left over to wander around, but not multiple hours.