We were a family of five (two adults, three kids - 12 years, 9 years, and 5 years old).
All of us loved the experience. We got an excellent forest experience with a very diverse set of plants, animals, birds, insects, reptiles, water bodies, streams and more.
Staying overnight allows more time to explore Corcovado and see/hear animals in the evening and early morning, and not just for a few hours in the late morning.
Please note that, as stated in the details of the trip, accommodation is a dorm - lots of bunk beds with insect netting for each bed, and shared bathrooms (which are reasonably clean and have cold showers). We all slept very well and enjoyed the food - which is served in a school cafeteria like setting.
Please note the following:
-- you are not allowed to being ANY food, including fruits, chips, bars, and other snacks. The ranger at the entrance of the park goes through the bags (not a details look, but does a quick scan) and will take away any food.
-- be very careful while entering the exiting the boat -- depending on the conditions (waves etc.), the boat can move suddenly and one may have just a few seconds to get onto the boat in each cycle (when the boat is steady for a few seconds, passengers get onto the boat and when the boat is being suddenly pushed out/in, passengers back off from the boat and wait). This gets tricky especially with kids. Also note that it is a wet entry/exit -- kids can get wet till above their waists, and adults can get wet till their knees, but may also get wet above their waists).
-- there will be a dedicated guide for each group (from 2 people to 10 people).
-- remember to bring a small day back-pack for water, rainwear, sunscreen, bug-spray. There is a lot of walking all through the trip, including an optional 4.30 am/ 5.30 am early morning walk to experience the forest around dawn.