Very much worth a visit. The history is amazing and interesting, and kids of all ages should love it, but especially those interested (or, once interested) in dinosaurs. The museum provide some excellent context and hands on activities. You can even see live scientists analyzing the cleaning fossils found recently. They're in a windowed room for everyone to see. (Cool to watch, but that would be some boring, painstaking work.)
Note that the outside (the actual tar pits) are free to visit as long as the gates are open. You're paying for the movie, which is great and provides some good history and context. The outside area is open to the streets, so homeless people (a real problem in LA) tend to make use of the green open spaces as well.
I wanted to see it since I was a kid (I'm 51 now), so I brought the family and they enjoyed it as well.