Perhaps they’re more aggressive because they found out they can push their parents around and get all the soft drinks they want. If they can control their parents with aggression, why not anyone else they come in contact with?
Probably all the pop kids drink indicates what the home is like — Mom (probably no dad around) is too busy and tired to deal with conflict with the kids about what to drink, and she won’t buy milk because it’s expensive and she doesn’t know why kids need milk because she dropped out of high school before having a home ec class, or else her school did not teach home ec anymore. I know punctuation is my friend but I am on a rant here.