August is a great time to see both nesting momma turtles as well as possibly seeing some of the baby turtles hatching and making their way to the ocean. Tortuguero is a really exciting destination for families who enjoy wildlife. Because you have 10-14 days, I suggest 2 nights here. A fun place for families is called Aninga Lodge. They include transportation from San Jose and all meals (buffet style) during your stay. Definitely check is out.
It's definitely a sight... The town is small, and really the only purpose of its existence is for one or two night visits to see the turtles lay eggs at night. It's a good trip to take, and a fun thing to do if you have the time but beware that the beach looks beautiful but the bugs will make it impossible to lay out of (something to do with the eggs attracting flies?) and make sure you take the bus out of San Jose early, I got stuck in a transit town for a night because I missed the last boats to tortuguero (the last ones are sometime around noon...)