This film is for parents, but might appeal to some kids. It's not perfect but I'd highly recommend it.
While some kids may enjoy the film - I feel like it's aimed at parents (The writer/director says he had a child and thought "What kind of parent do I want to be?"). Unless your children are the ones from this film (and kudos if they are!) then half the dialogue will go over their heads (I struggled and I'm 37yo and have studied philosophy).
The experience of watching this film is amazing just for the fact that you can watch it. People rarely talk about this stuff. It's great to have a high profile star getting these topics front and centre - consumerism; poor school systems, home-schooling, living off-grid, accepting/rejecting "the norm" and how will the choices you make as a parent impact your child when the enter "the real world"?
The film opens with a young man killing a deer for food - a lot of fuss has been made about this - but basically it sets the tone for the film: no holds barred. It's not all full on of course, there are some laugh out loud funny moments and some very sweet heartfelt parts as well.
Viggo does a great job portraying "Captain Fantastic" - Ben, a father raising his children off-grid in the forest, teaching them to be self-sufficient, learning from books, speaking 6 languages. He gives a nuanced performance - Ben is neither saint nor cult leader - a little from column A, little from column B. The film does not shy away from his hypocrisies - he is not always right and he realises that.
The kids are all great in their own separate ways, with some stand out moments, though they are definitely over-shadowed by the adult cast. Steve Zahn and Kathryn Hahn are great as Ben's in-laws, providing the "real world" family juxtaposition. And Frank Langella and Ann Dowd are fantastic grandparents, playing devil's advocate while realistically representing what the majority of people are probably thinking!
The film is not subtle, and sometimes that feels a bit laboured - but then again, how many films delve into this kind of material? There's little to compare it to!
For a great summary from a 16 year old who was homeschooled and realtes to the characters read: https://www.commonsensemedia.org/users/tamago101
The film did remind me of "Into the Wild" - where the main characters choices were not celebrated but just presented. The film wasn't a recipe for what to do - rather presented as very interesting concepts to consider (that film was based on several true stories to boot!)
My biggest gripe - the stupid title! Everyone assumes it's the latest B-Grade Marvel Comic. To me it doesn't reflect the content of the film, it doesn't seem ironic, and ultimately since it's an ensemble piece with many great characters - it does them a disservice to just focus on dad.