We usually pick a relaxing, family friendly place and stay for most of a week. Always get at least a one bedroom (kitchenette suite at a hotel, or vacation rental for longer stays) so that whomever is NOT napping can watch TV and lounge around the rest of the unit during naptime. A water view is nice
Schedule activities in the morning after breakfast so you can have fun before lunchtime. Then do the pool or small town explorer stuff, taking it easy before an early dinner.
Our kids have been pretty good about getting worn out building sand castles, chasing crabs, learnign to walk etc. and then falling asleep on the beach (under the umbrella, on a blanket, with a nice warm pile of towels) so we often were able to stay out on the sand most of the day.
Caveat: Once I set up my baby monitor outwards on the balcony so I could walk around the side garden and waterfront of my hotel near the room while baby was napping. DH came back from exploring and since the baby was still napping we enjoyed a little afternoon delight...later I realized I had left the monitor on...broadcasting from our room out into the hotel courtyard! D'oh! Don't do as I did!