maybe I just haven't gotten there yet. I'm a big kid at heart though so I totally revel in their joy, and when it comes to playtime and fun I have no desire to say no. maybe its because my own childhood was so lonely, boring, and without interaction... in a way sometimes I feel like I am getting a chance to be a kids for the first time. Of course, I have to be mommy too, its a fine balancing act lol, I'm always Mommy first, but I'm definitely down to enjoy the things they enjoy.
I like spending time with my kids, just...hanging out. I like taking them for walks and answering their questions, and if I don't have a million other things to do (not often, I'll admit), I like having them bake with me and such. I love taking them to the park and being their audience and/or climbing around with them. I enjoy playing board games and card games with them (as long as they're not getting too upset over them). I just don't like having my brain pushed into reading at the right speed to speak out loud, or having my creativity and imagination put into the box they want it in. I actually thought, before I had kids, that I'd enjoy the being a kid part of it...but it just hasn't worked out that way on many fronts. I don't feel like I'm being a kid when I'm getting yelled at for saying the wrong lines or whatever.
I always wished I was more like you, especially when ds1 was an only child. I wasn't very good at playing with him. Fortunately, dd and ds2 like to play with each other, so it's not as big a problem for them that I'm not usually into it.