I normally don't like movie musicals. The main reason for this is that without being in the audience, a lot of the time the performers seem to give off no energy and kinda look dead. There are a quite a few exceptions, Chicago almost (almost) works better on screen, Into the Woods perfectly captures the wit and darkness of the stage production, Mamma Mia is fun and the only thing wrong with 2012 Les Mis is Russell Crowe. However, there are many examples of really crappy movie musicals, The Producers fails to capture the screwball energy it should, all the NBC live productions feature at least 3 weak links, and this has no good performances, is so freaking over the to cheesy, and has no energy from anywhere. The only thing that makes me not rate this 1 star is that it has a so-bad-it's-good theme (that gets really old fast) and really great music. Buy a cast album instead.
If telling a kid this won't help, then the only thing wrong with tis is one number where Joseph's boss's wife tries to seduce him, and then has what I think is some kind of orgy with him after he won't comply. Most kids won't pick up on the sexual side, but from personal experience, I can tell you that there aren't a lot of things creepier than a 5 year old constantly repeating the line "come and lie with me in love" (a line from the movie.). Plus, Joseph's dad is very obviously a polygamist. Not really OK for the youngest, but the oldest will hate it.