I had all three boys at my house the weekend of the 24th. At one point, I was working on getting the eight-year-old to build a tower of megablocks (think very large legos). If I handed the blocks to him one at a time, he would stack them up. The one-year-old was watching and wanted to participate. It sill surprises me when he does that. I heard that kids were supposed to do that, but I never saw it with the older two. I gave him some blocks to hand to his older brother.
We finished building, and I went off to do something in the kitchen. A few minutes later, I noticed the one-year-old toddling from the eight-year-old's room into my room with a megablock in each hand. I followed him. I found the eight-year-old sitting in the rocking chair in my room with a tower of blocks in his lap. The one-year-old handed him the new two new blocks, which he added to the tower. I stood and watched while the one-year-old carried in all the blocks and his older brother stacked them.
I think this is the first time I've seen the eight-year-old engaged in any sort of cooperative play with toys with another child. He wrestles with the eleven-year-old, and he will sometimes play with toys when directed to them by an adult. At one point during his ABA therapy we devoted many weeks of therapy to trying to teach him how to play with a toy car, blocks, and a doll. At school this year they were working having him play at the same table as another child--not interacting, just tolerating the other kid's presence. I can't remember seeing him play with toys with another child.