Tough one. As has already been mentioned, there has to be a clear line where the kids are involved - that is to say, are you going to be there for them or not?

If it's the latter, that's not an issue. Declaring that from the outset isn't a drama - single parents aren't suddenly robots and enjoy the affection, sex, and friendship too. There's no expectation beyond that and a few hot dates, and if it does start to cross red lines then there's a clear reason to start nosediving it into the sea.

I think leading a parent on though to the point where you're introduced to the kids and become a part of their life, and then drop the bombshell that you're after the casual or physical side of things means your actions have caught more than just the pair of you in the blast, and that just sucks.

Honesty isn't hard, and most of the time it's pretty hot!

e for context: I use "you" in the assumption that you're looking to date a parent - reframe it to your own view :)