Surf, if you're looking for a day trip from Pittsburgh, the 2 closest options are Seven Springs, like zip mentioned, and Hidden Valley. From Pgh, Seven Springs and Hidden Valley are both about 1.5 hrs away and in the same general area. I'm pretty sure they are just on opposite sides of the mountain.
Never been to Seven Springs and only gone twice to Hidden Valley, but Seven Springs is definitely the more popular of the 2 and has more bells and whistles at the resort. Hidden Valley is pretty much just the slopes and snow tubing. Not really much of a terrain park and a pretty basic lodge from what I can remember. Hidden Valley lift tickets are slightly less ($10?) than Seven Springs. My wife and I go/went to Hidden Valley mainly because we're beginners, it's a little less crowded there, and the price.
No kids here, but I'd bet that Seven Springs has more options for 5-6 yr olds.
Oh, and I just saw that Blue Knob resort is about 2.5 hrs east of Pittsburgh. Never been there and know nothing about it. Still doable for a day trip possibly. Website is showing only 11 of 34 trails open.
[This message has been edited by mamor012 (edited 1/9/2012 9:41a).]