Please check this web out for the resort that you are looking for http://www.anywherecostarica.com/hotels/family

I stayed here without kids in June, and it was very nice. I think Bahia del Sol would be fine for children, especially older ones who might enjoy ziplining, snorkling, or nature trips. Howler monkeys and parrots are often right outside the hotel rooms. The beaches are okay, but not perfect -- you have to share them with cows -- maybe that's a plus? The ocean is warm, but there's also a lovely swimming pool. There are good restaurants fairly close, but the hotel food is excellent if you don't want to go far. Overall: not fancy, but nice.