We spent a week at Leaves and Lizards with our kids aged 10 and 14 and had a fabulous time.
We had a huge cabin with walls decorated with toucans painted in bright colours. The cabins (not that you'd know there are any others) are on a slope and our huge veranda overlooked the top of some secondary forest and of course the Arenal volcano. We could watch the sunrise over Arenal without even getting out of bed thanks to the huge windows all along the front of the cabin. One of the first things we saw each day was a flock of parakeets and a pair of woodpeckers. A sloth lived in the tree outside, and we heard howler monkeys.
The owners, Steve and Debbie, and their manager Oscar, were very welcoming, making a special effort with wheat free food for the kids. I've never had so much fun at breakfast - they put out baskets of food to attract the birds and you hardly know where to look, there are so many. Parakeets an aracari and honeycreepers have been the prettiest. Steve brings his tame parrot into the dining area (I hesitate to call it a room as its missing a wall) and we fed her with watermelon seeds.
We hired a car in San Jose and drove ourselves, which meant we could reach the various local attractions very easily. We went zip-lining, visited Arenal Volcano park, had a great day trip down the Coco River on the border with Nicaragua, and went horse riding.
The horse riding was the best I've ever experienced. Our hack went through knee deep mud, rivers, rain forest paths and more open cattle fields full of tussocky grasses. We rode for about 2 hours to a waterfall, swam for about half an hour in the deep pools, had lunch (tortillas with cheese and ham) and then went 'the long way' back. The horses were fantastically well behaved and surefooted. Debbie has trained them using Natural Horsemanship techniques, with an emphasis on working with horse psychology and I'm a convert!