To be fair, though, Jim is the last of the Chapman siblings to have kids. Sam is an aunt three times over by now. So, yeah, why would Jim's particular child be exciting?
I'm no Sam-stan but I found her reply kind of funny and in a way refreshing. Not everyone likes kids or is excited about kids. Good for her for being honest about it even if she gets called bitch for it. The comment about her own kids is obviously meant to be taken as a joke, although I know people who love their kids but admit to not having liked them when they were actual little kids because, guess what, they don't like kids.