Wouldn't kidnap the kid myself, would contact Child Protective Services and get the kid out of that situation and given the treatment it needs. When the actions or inaction of the parents are grossly detrimental to the welfare of the child, there are systems in place to deal with that sort of situation for a reason.
Freedom of religion doesn't even enter into it. One's freedom of religion extends only as far as the person themselves; it ceases to be a factor the moment it abridges the rights of another person. In this case, the parents' right to religious freedom would be intersecting with the child's basic human right to life. The kid's age doesn't factor, either - guardianship of a minor doesn't mean that the minor is property, they've still got rights that are protected under the law.
Freedom of religion doesn't even enter into it. One's freedom of religion extends only as far as the person themselves; it ceases to be a factor the moment it abridges the rights of another person. In this case, the parents' right to religious freedom would be intersecting with the child's basic human right to life. The kid's age doesn't factor, either - guardianship of a minor doesn't mean that the minor is property, they've still got rights that are protected under the law.