Should children of people who belong to cult organisations like westboro baptist church, KKK or MAGA be removed for their own safety?

You're going down a slippery slope here.

But you really think Trumpers should have their kids taken off them?

Not sure that this is the right path. But parents who indoctrinate their children with these ideologies are vermin.
I do not think MAGA is anywhere near as bad as Westboro or KKK.
Should not all US citizens strive to make America great again?
Is KKK still active?

Yes, definitely