How could a child be stuck in a microwave? I think they'd have to be a premature baby to fit in and it's very unlikely.
I remember the Satanic Ritual Abuse blood libel of the 80s and 90s. A lot of the most lurid allegations were found to not have taken place, and a lot of innocent people were accused, most of whom weren't even Satanists or any kind of alternative religion.
Abuse is a crime, but being into alternative spirituality, including Satanism, isn't.
Also, Satanism isn't the same as witchcraft/paganism. If a pagan group involved in child abuse is found (which is rare) they are labelled Satanist in the press, when they're not, they're into witchcraft or Thelema (like with the Kidwelly cult.)
Calling them Satanist is untrue, sensationalist and libelous towards Satanism.
Obviously, abusers can be found in any religion, and if these have committed abuse I hope they're treated accordingly by the courts.