She was probably teaching them about Jesus and other things which go against the state.
There’s probably a lot more to the story than we’ve heard, and police are probably only in the early stages of figuring out the whole story. Most likely the children really are a lot safer in state custody right now. What’s unlikely is that there is no prior connection between the person or persons behind the abduction, and one or both of the baby’s parents. Kidnappings in violent home invasions by total strangers are rarer than rare.
Per the mother, the woman who did the abduction called someone right after grabbing the baby and stabbing the mother and said “The job is done” and that the mother was “dying”. Either the mother made this up and is lying to police for some reason, or the abductor was working on behalf of some unknown third party whose connection to the family (if any) still hasn’t been determined. It’s entirely possible that the parents are involved in drug trafficking and/or gang activity and that they were targeted due to that, and if so, all the children are a lot safer being out of their parents’ home.