Food makes a big difference in my
kids behaviour. Mainly Omega 3 (Udo's Oil) in a smoothie every morning, and a little protein every few hours, even just a couple of small bites of meat, a few nuts or a boiled egg. They argue less, are calmer, cope better, and more cheerful when I do this.
Especially if behaviour seems to be always at certain times of day, I would make sure they have that little bit of protein a half hour or so before it would usually happen.