I spent there 3 years.What worht to see:
1) Old San Juan
2) Rain forest( El Yunkue) ,they have a lot of bus tours, but it worht to rent a car and go by yourself. It is a lot of waterfalls there. To see the best you have to parc a car and walk approx. a mile through the jungles.
3)Culebra, Flamenco beach - little island near PR. You can take ferry from Fahardo (about 30-40 min). In the rating "the best beaches of USA " it was on the second position.
4)Arecebo laboratory - the biggest telescope in the world located there. It might be interesting for your child. They also have a musiam over there. If you ever saw movie"Contact" with Jodi Foster, it was filmed there.
5) La Paguerla - phosphorescent beach in the S-W. They have night time boat tours, so you can see "shining" water.
6) they have a lot of one-day tours on the sail-boats. They take you on the corall reefs to dive or snorkling(???? not sure how to spell it), serve you a lunch , and take you on some private beaches.
This is that came first into my mind. If you have more questions, feel free to send me e-mail:
NataliyaF@aol.com