JeffT: just because it doesn't like how they think, or what they believe.
That is an understatement
The children could be removed because the parents were involved in illegal activity. Not any different than many countries. That happens in Canada and the States too.
Want to risk losing your children? Do illegal things.
In Russia, engaging in practices that define you as belonging to an extremist (banned) organization is simply an illegal act. THAT is what will get children taken away. Doing things that are illegal will risk your children being removed from your care.