I’d recommend the musical. My family saw it when I was about 13, and my sister was 11. I think some of it went over our heads, but it was visually and musically appealing.
I think the story does have good morals overall… I remember one time a priest quoted the line, “To love another person is to see the face of God.” My sister and I immediately remembered that from the show. The story is overall about love, redemption, charity, compassion for the poor, and mercy.
There are some mature themes:
*Some rather crass scenes with prostitutes and the very crooked Thenardier family.
*Some battle scenes and deaths–nothing graphic, although there is a scene where a child gets shot.
*The scene where Officer Javert commits suicide by jumping off a bridge (again, not graphic, but still clearly a suicide).
*The scene where Marius grieves for all his dead friends and feels guilty that he survived.
*Some pretty mature philosophical/moral themes.
All of these things might need some explanation for your children, depending on how old they are. Seen in context with the whole story, they are necessary elements (i.e. not gratuitous).
The book is definitely for an older audience… it’s very slow, long, and dense. The feature film was dismal as I recall.
Hope that helps!