Animated movie with sack puppets with numbers on their back

When 9 first comes to life, he finds himself in a post-apocalyptic world. All humans are gone, and it is only by chance that he discovers a small community of others like him taking refuge from fearsome machines that roam the earth intent on their extinction. Despite being the neophyte of the group, 9 convinces the others that hiding will do them no good.

When forces within and beyond this world conspire to snatch his son away, a father resolves to do whatever it takes to protect him.