As a teacher, we had classes on cortisol and the effects on children. We were taught methods to deal with the issues.
For instance, some teens look at an accidental bump as an aggressive move. This is something that can be discussed and dealt with.
Daycare may have a high cortisol effect.
I worked with young children and accidentally found something that made a huge difference. It was "fake mother" .
I would take a picture of the mother ( I worked with people in poverty so many were single mothers).
I laminated the picture and gave it to the child to hold. That seemed to calm them a lot. Whenever I found it , I would go put it back in the child's locker. Throughout the day, children would take out the picture, then leave it when comforted. Normally, I expect children to take care of their own possessions, but in this case, I took care of it for them as I did not want "mother" to get lost.
Another thing I learned was that children that need something are the only ones who will need it.
For example, I did not allow any toys from home, except sometimes. Sometimes a chid needed some stuffed animal or other comfort thing. I would explain to the children that so an so needed the object because s/he was sad or whatever. The other children accepted it and the next day may have brought their own object.
The children who did not need their object quickly forgot about it and the others were not even interested.
We also had pads with little bumps on them for children to sit in. Or objects to squeeze if they were upset. There are all kinds of strategies to lower cortisol.