We saw it last night with my 12 year old daughter. I personally would not worry about taking a 10 year old and probably would not worry about taking a 7 year old. The violence isn't bloody, for the most part, and while there are some scary scenes (intense battle), most things are implied (e.g., to torture the princess the wizard waves his hand near her and she grimaces--nothing too explicit). Of course, like most people I hate to give advice like this because your boundaries for kids may be different from mine! I have a 10 year old niece I wouldn't take because she's extra-sensitive to such things.
The movie was very bad, though. I expressed this in more detail
here.