Depends on the kid
Various things push me towards saying don't let your kids play, because of gore, violence, and the community online is rather inappropriate and disappointing. They upload lots of levels that can be scary, sexual, and more content kids shouldn't be exposed to, as I myself don't play this game online. However, in most platform' s settings you can turn off blood/gore. So that's a "happy' note. Hard game. Very hard.