We have regular family holidays in the Outer Hebrides (as we used to live there, have a house we rent out there, and we always have a tremendous time whatever the weather). Beaches clean and outstanding, great fresh local food, good activities for children, especially active ones.
But our best ever family holiday was 3 weeks in the Dominican Republic 2 years ago. We avoided all-inclusive, rented an apartment in a small complex with a pool, shopped locally, ate out plenty in cheap, quiet restaurants, dc learned to surf and snorkel, dc and I had Spanish lessons, dh and I learned to scuba. It was expensive but we loved every minute of it and I'd happily recommend he surf school, diving school, Spanish school and apartments to anyone. It was in Sosua and Cabarete, near Puerto Plata.
For us it was great as it was active, lots to do, and good because we met locals, weren't just stuck in a resort. It was a treat for dh and I for our 40th Birthdays instead of presents and parties. We'd love to do it again sometime!