This movie was o.k. to watch as a family. A few darker moments for younger kids (7-8 year olds) though some of the younger kids might enjoy the suspense--the main character's father is a bit scary. Some negative messages about stealing and about parents/caregiver's being unpredictable & kids trying to control their own situations by running away. (Other main characters, Prosper and Bo, run away from an Aunt who's trying to adopt only Bo after their mother passes away.) But it is a fantasy in many respects, the beautiful scenery of the city of Venice helps that element along.
I think kids younger than 7-8 wouldn't be able to follow the story line/find an interest in it. I think kids older than 12 would find it unsophisticated (even though they might secretly enjoy it.)