Our family of four (including a 12 year old boy) stayed at Posada Wiwa, Sector Los Naranjos, one of the Posadas Turisticas, for 3 nights a few weeks ago. It is outside the Parque, on the eastern edge (it took us ~ 30 minutes to walk to the entrance), close to the Caribe highway. For our family of four it was ~ $150/night, but it is less for fewer people. It was challenging for us to make reservations, but worth it. Catalina cooked us delicious breakfasts and dinners. They have two whistling parrots. The posada was clean and very tasteful, with mosquito netting. Do bring bug stuff for hanging out on the porch, in the hammocks, or eating your meals on the family's porch.
The host family was lovely and took good care of us, showed us to the Los Naranjos beac, a 10 minute walk down the dirt road, where the younger family member surfs -- careful, there can be rip tides, the waves were very powerful (too powerful for our 12 year old). But the clean, shallow, sandy Rio Piedres enters there too (just below the luxury Barlovento) and was a great swimming spot for our kids. Truly one of the most beautiful spots I've ever been too, with the pounding surf, calm river, jungle vegetation, amazing rock formation, and the Sierra Nevadas in the background to the south. Stunning.
If you are not staying in the park, you have to pay for each day you visit. We thought it would be like US National Parks where your pass is good for five days. So we just spent one day in the park. Get there early so you don't have to wait in line, and have your passport numbers with you. Take the minibus (for a fee) down to the main parking area, and then we took the hiking trail to Arrifices. Very nice, dry, good board walk, some interpretive signs. To stay out of the noon time sun, we took the horse trail instead of the beach from Arrifices west, which gave us great views of monkeys, and a visit to a great panderia (the chocolate bread is delicious). We swam at La Piscina, and two of us swam out to the reef where there is some excellent snorkeling. If you enjoy that, we'd suggest bring equipment from home.
Have a wonderful time!