My own two children ALWAYS do this. They have done it from a really young age, well my oldest has, my youngest has just gone along with it. They call it "making piles". My oldest is actually quite obsessive about this at times, and gets really upset if anyone touches the pile. I try to discourage it during daycare hours as she literally would try to take every single toy in the room and pile it up. She doesn't do it as much any more, but when she was younger she did it pretty much every time she played. Sometimes she would pretend the piles were different things (a cake, garbage, decorations, etc).