Quoting LinzKae:" When do they start sitting in a walker and playing with the toys? I was thinking about getting a pack n play and some clothes and maybe a walker."
Once they can grasp stuff (usually around 3 months) they start playing with toys a little. I put my kids in an exersaucer around 4 months I think it was. They didn't have great upper body control, but they'd touch the toys and stuff.