I think both little boys were bored, and given that scene on the metal steps, they didn't have enough supervision. It looked like one loud, long, boring day for two little children.
I must also say that letting children walk or run
with those lollipop sticks dangling from their mouths is a disaster waiting to happen. One fall and ... ugh! They should only have them when seated & supervised.
I didn't care for Alexander's letting the door practically close on his brother, but if no one corrects him ... and it sure didn't look like anyone did. "Brattiness" is the end result of no discipline and lack of supervision. So I don't really blame anyone but the adults in his life.