We went a few years ago with TUI to Costa Rica with kids a similar age to yours will be and all loved it. We did it as 2 weeks at the hotel but with trips out every other day which worked really well as the trips were amazing but long days. There was lots to do at the hotel, swimming, kayaking, windsurfing, beach, beach volleyball, water volleyball and it was surrounded by rainforest so there were raccoons, a coati, monkeys, gecko etc wandering round the grounds. Food was excellent. We were at RUI Guanacaste and lots of trips out from there, often takes 2 hours to get to places but driving through rainforest etc. The RUI was good but it was lively, nice rooms, amazing food with waiter service every night if you wanted, great sporting activities included but definitely on the lively side and beach was more for sports than sunbathing but that suited us. You could still sunbathe but was a bit wild looking. Not sure how much covid would have affected things but Costa Rica is somewhere we would go back to and due to uncertainty would book with someone like TUI again, had a nightmare getting refunds when booked directly with hotels etc for 2020. Would have thought you could get sailing and snorkelling from hotel either directly or on trips.
We did waterslide through jungle, ziplines through rainforest, active volcanoes, trips to see sloths, horseriding through rainforest, kayaking in sea, Arenal volcano and spa hotel, hot springs, beach volleyball, botanical and butterfly gardens, saw raccoons and coati and toucans and monkeys and sloths in wild. Went to Diamante, just next to our hotel.