Don't expect to meet the kid(s)
Unless you bump into mother and child at the farmers market, you aren't likely to ever meet your F-buddy's offspring. Don't be offended by this. Moms don't want to confuse their children by meeting every casual hookup. Plus, it is a big step that doesn't make sense in a casual situation.
"Wanting to have fun... doesn't automatically mean I want him to be my new baby daddy/stepdad" -- Megan, 30
"The biggest rule, for sure, is that they won't meet my kids. I don't even really talk about my kids, except in a very general way... Generally, though, if the relationship is casual, I have found in the past that there's little interest in knowing about the kids anyway." -- Micah, 41