We are 2 adults and 3 kids - ages 11,10,8. We spend 5 days in Puerto Jimenez. While we loved it there, I think 3-4 days would have been enough and we left a day early bc we ran out of what to do and one more jungle hike was not in the cards. I recommend staying in Jimenez. I looked at Iguana Lodge and went to see it and was SO happy not to have chosen that. It is on a bumpy road, is isolated, slightly washed out looking for the money. For us with our kids, it would not have been ideal. Also no need to stay in Carate - too remote and nothing to do beyond the park.
As for the park. We did the 18 KM trip BUT we got through 11 kms only because our kids were waning and the guide from Ficus (amazing!)- named Luis- said that the big mistake a lot of people make is pushing through the 18 kms. So we turned back at the river. It was an amazing trip. Paid $195 for the 5 of us while other tour guides wanted $250 and up. We saw toucans, sloths, anteaters, coati, monkeys, tons of birds.
Another day we did horse back riding with Rancho Tropical and loved it! It is expensive though at %75 per person but we loved it!
Another day to the water falls at Matapalo - not the King Luis ones - the closer ones where you park right after Martinas bar. That was pretty great. The hike is mostly through the river so bring water shoes.
We did the zip lining at Osa Palmas which was great. Nowhere near as high as other lines. But great for novices like us.
One more day we went to the beach - MEH! I would not go to Osa for the beaches. They are either too dangerous OR they are just not inspiring.
All in all we had a great time BUT PJ is a great base but nothing more. The restaurants are so so. There is nothing to do. It is hot and dusty. IF you are a couple - then maybe some romantic spot would be great but as a family of 5 - we were ready to leave by day 5 even though we planned for 6 days.