Today at the beach I watched Corbin and Brian work together to build a long trench towards the lake so they could dump water and watch it go down it. This is something they started last summer and did on almost every single beach trip. Today was the first time it really had a profound effect on me.
Generally the boys don't ever play together. Sure, they almost always insist on being in the same room playing- but Brian is usually lining up his trains and Corbin is playing Bakugans. They don't talk to each other while playing and they don't have a common goal in mind. It's basic parallel play that is normal of toddlers. At the beach though, they had a common goal they were both working towards. Sometimes Corbin would give directions and Brian would follow them. They were laughing together and having so much fun. Everything else on the beach went into slow-motion as it sunk in what I was seeing. I, then, gushed to Josh about how what we were witnessing was so important. It was a much higher-cognitive level of play- cooperative play. He has it in there, it's just finding those keys to unlock it.