I’m with @Randy on this one. To an extent. He doesn’t deserve to see the kids, but he should be the ones to tell them that he’s in trouble.
When my birth dad went to jail for sexual abuse of me, I was six.
He called and my mom told me he had something to tell me. I don’t remember all of the conversation, but he told me that he was in jail for “abusing his role as a father”. He explained that nobody should be touched inappropriately and that he broke a lot of rules with what he did to me. I still didn’t know anything was wrong with what happened at this time. I understood what he was saying, and didn’t ask any questions after that. I accepted that he broke the law and was in jail for it. I’ve always understood the concept of jail.
But it really depends on the ages of your kids, and how well they handle things.
There’s no definite answer to this. You know your kids better than we do. Every case is different. It’s what you feel comfortable with, and what your children will understand better.