I don't know what is wrong with these two today

We went for a long walk, played ball, they had dinner and just started being little troublemakers so I gave them each a kong with rewards in it. That worked for about 2min then Hallie decided she wanted Simon's and vice versa.
Hallie started screaming at Simon and he lunged on her, had her on her back and they were fighting. I walked away and they immediately stopped but both got a time out.
Maybe it's the dreary cold weather? I think tomorrow we will all bundle up and walk a few miles

A tired baby is a happy baby, right?