Christian Science is a strange sect of Christianity that foregoes all medical intervention, relying instead on faith to cure illnesses. Many children have been harmed by this, as parents have refused to give their children treatment, and this has often led to death or disability. CHILD, Inc., a charity to combat this element of Christian Science(and other neglect), has examples on its website of harms done by the religion.
Obviously, attempting to heal your children with "faith healing" is wrong. For a start, there is no evidence to suggest that faith healing works at a level better than chance or placebo effect. One would think if it was effective we would use it is medicine, for a start.
Secondly, the people are responsible for their children. They are their guardians, and are supposed to do what is in their child's best interests. Obviously, this would be taking them to hospital when required.
Thirdly, the child is not rational enough to decide what its religious beliefs are. Forcing a religious belief on a child by making that decision for them is wrong.
If an adult decides to snub medicine in favour of faith, that's their decision. It may be an idiotic decision, but it is up to them. But people should never do these kinds of things to their children. It truly is one of the worst sins of omission.