Pacuare is a great trip...the Sarapiqui is also fun. The Reventazon is also fun but if they won't let a 13 year old on the Pacuare they probably won't on the Reventazon as it is a step up and has some solid IV's to even V depending on flows...I can only speak of those 3 from personal experience. The last time I was down there we did zip-lining and then rafted the Sarapiqui and it was a lot of fun. Some III's but nothing too much more than that, which is OK cause it gives you plenty of time to sight see and check out the toucans, monkeys, etc.
Don't want to dissuade you from your existing plan but Arenal is no longer an active volcano so it has lost some of it's luster. While it is still a cool spot, it doesn't have the glowing lava at night anymore.
One jewel I discovered a couple years ago was the Hacienda Guachepelin which is in the Guanacaste region near another volcano with a great hike to a crater, Rincon de la Vieja. While whitewater tubing is a fashion faux-pas on the Buzz the Hacienda Guachepelin has the funnest tubing I have ever done...you take a horseback ride to the river, get on a tube and go down some class IV's rated on the international tubing scale. Seriously it's a hoot. The Hacienda is all about the eco-tourism that Costa Rica is known for. In addition to hiking to a crater, horseback riding, and tubing, you can also do waterfall cayoning, zip-lining, and mud baths by the crater hike, etc. There is a short walk to a waterfall from the Hacienda as well. The place is a kick in the pants for your whole family...check it out:
Hacienda Guachipelin Hotel Rincon de la Vieja Guanacaste Costa Rica
From there the area of Tamarindo is not too far away if you wanna get into some surfing, fishing, disco-tecaing, etc. Tamarindo has grown over the years and is pretty touristy but still a fun spot with great beach breaks at Playa Grande.
Have fun, you really can't go wrong anywhere (except maybe Jaco) and Costa Rica to see it all involves a really long time spent down there or to just return as often as you can!