Peaceful Play

From what I can tell, these two adore each other. But they don't always play sweetly together. It's mostly their ages, but there is generally a fair amount of tussling, bumps and screeching.

Thus I was a bit surprised today when they played together for two hours straight without a single incident. They shared (SHARED!) a coloring book, had breakfast together and formed a marching band. I'm suspicious, what are they up to?