I just thought of something I've done several times when I was young (19, 20 years old). I had a few lady friends and acquaintences who'd hit me up, and invite me over for a quickie. Some of them were single mothers.
I can't even count the number of times I walked into the front door, and the chick who invited me over popped in a VHS tape for her kids, as they watched me follow her into the bedroom, and then 20 minutes later they see me come out of the room and head for the front door.
That was over 20 years ago, and I would never have been doing this if I thought the same way back then as I do now.
The thing is this: I'm fairly certain that in none of these cases was I the first guy that these kids had seen doing this, nor was I the last.
Now I can look at it from the perspective that, regardless of a woman's marital or parental status, she has sexual needs to meet. And then I don't have to feel bad.
The other way to look at it: does this negatively affect the way they view their mother? Because that's something I think about when I look back on this.
With a two parent household; children seeing mother bringing in random strange men to have sex with isn't a thing. I mean, it could be in theory, but I doubt that's the case in practice much.