If I had to guess, this sheriff in particular is very old-fashion when it comes to relationships, marriage, children, divorce, etc. It seems to be passed down from generation to generation and seems to be nearly impossible to break the cycle. It's all they've ever known growing up and it seems small communities/rural areas turn a blind eye if they see or hear that type of behavior (or practice that behavior in their own life). Plus, he's only heard one side of the story...who knows what stories SM has been telling.
I'm scared SM, if given the opportunity, will try to convince the kids that CM was the "bad guy" and he was saving them or something equally ridiculous. He strikes me as very manipulative (if you leave I'll kill/hurt you/kids). Good dads don't threaten to harm their children. Good dads don't kill the mother of their children and certainly not while their children are in the same home.
I'm with the others who feel SM only cried because he was busted, not because he was sorry for killing CM. He was probably crying because he had to sell his precious car to pay for a lawyer/bond.
I also think an 8 year old will probably put things together soon if he hasn't already, or if the family hasn't told him. I'm sure my 8 year old daughter would immediately think if someone went to jail she knew, it was for hurting or killing someone. You can shelter them from the media, but you can't shelter them from their own logic/knowledge. Kids are smart, sometimes too smart for their own good.
When it comes to the kids visiting SM, it should definitely be up to the kids, but I feel the kids have every right to know why he's in there before making that decision. Maybe that's harsh, maybe I'm wrong for thinking kids deserve the very limited truth, but I feel the kids would not want to see him if they knew he was the reason they would never see their mom again.