Why can't they be like that at home?

Wednesday morning I barely get home from dropping the kids off at school and the phone rings. It's the school. "Mommy, I forgot to tell you last night, I'm out of lunch money and my teacher said I have to call. " Also my son couldn't find his gloves and has taken the good ones to school which I only like him to use for skiing. After morning naps and finding the other gloves I pack up the two youngest and go to school. After dropping off the money for lunch, I go to my son's classroom and find he is currently at lunch. He begs me to stay, so I buy Imogen a lunch. My oldest's class comes while we are sitting there and she and here friends sit with us too. They are all so excited to sit together. After a bit my son show his 4 year old sister where to take her tray and then leads her by the hand out to recess. When I catch up with them, he is trying his hardest to lift her onto the swing. He only weighs 5 lbs more then she does, so is not very successful. Once I lift her on he insists on pushing her and then takes her up the slide and reassures her that it's not too scary and even defends her against kids who just want to push her down the slide because she is holding up the line. They were both sad when he had to go back to his class. These of coarse are my same two children who fight about everything when they are home.