It's appropriate, but the length is an issue--two-plus hours is a LONG time for 3s and 4s to sit still and be silent. When I saw Lion King, there was a family with very young kids--about that age--in front of us, and it was really tough for us to watch, as the kids were climbing all over the seats, asking questions, etc.
I work in theatre, so I'm all for taking kids to see shows, but please consider that others around you want to see it, too. Can your kids sit through an entire movie without disturbing the other patrons? If so, they are probably good to go. If not, please consider waiting two years or so, when they will get a lot more out of it.