This is a movie about a kid who leaves her birth family.

Not a kid who find that they have a secret lineage or something that allows them to find their ‘true family’ - this is a movie about a kid whose true birth family is made up of bad people. So she gets out. And that is played as the right thing to do. She isn’t punished for it or made to feel bad about 'abandoning her family’. There isn’t an underlying 'but they’re your family and you have to love them’ or 'they’re your family and they love you even if they don’t show it well or do hurtful things’ message of the kind that I see OVER AND OVER AND OVER AND OVER in media. Matilda gets out and livess happily ever after because of it.