Dating single Parent? (What is the Expertations)

Right now I'm more or less lurking on my dating site. Checking out profiles to see who's out there and what I want in a partner. 

I suppose it should come as no surprise that at my age and the age bracket I look at (25-40) many many many women have children. Since I'm jumping in to this after an extended break, this is unfamiliar territory for me. I'm not opposed to it but it does bring up some concerns.

When dating single parents what are some of the expectations we should have? What things should be avoided? What things accepted? Anything to watch out for?

I watched my sister date and then marry a single dad. Among the many reasons I hated him as I've hated no other human being is she immediately became their de facto mom while he ignored them and her to play video games with his friends. Now she's with a great guy who also has a kid but who he takes awesome responsibility for.

Is this a common issue for women dating men with kids.? Any guys get pulled into being a dad more than being a partner?

One issue that I think affects pretty much only men is showing affection to these kids. My last job was working with kids in a retail environment. I was the only guy among many women coworkers and I felt as if I had to be constantly aware of how I was interacting with them lest someone get the wrong idea. My coworkers did not. I understand why. Its not exactly fair, but I get it.

Has this been an issue for you when you started dating a single mom? I imagine as she gets to know you and trust you its less of an issue, but how have you dealt with it?