It's lovely that you think of childhood and school days as carefree.
For many, childhood is not carefree at all.
I suspect this is the case for a much higher percentage of children than you would guess if you are from a stable family background.
If I was back at school today perhaps I'd have a chance of speaking up about how anxious and depressed I was, the suicidal thoughts, the eating disorder.
Perhaps that would save me from another 30 years of trying to deal with it?
I think a lot of children had the beginning stages of mental health issues when I was at school in the 90s but we just didn't talk about it and 'got on with things'.
This is seen as more 'resilient' but is it? Or is it just ignoring problems that could have been resolved earlier until you have a breakdown in your later life?
People often divorce the thoughts around 'why are so many children depressed or anxious or acting out through angry/bad behaviour?' from the frankly horrendous stats of how common it is to be sexually, physically or emotionally abused or to grow up in a household where a parent is/has been emotionally or physically abused.
Then add on top of this the number of children growing up with parents who are drug addicts or alcoholics (including the many functioning ones).
On top of that add on the children where there's nothing that would count as 'abuse' but that are growing up with parents who just lack basic warmth/parenting skills.
Children who have been adopted, children who have one parent who is absent or not consistently in their lives. Children who have been bereaved.
Sadly there is lots of trauma in our society. Many of the children you know and that your DC are friends with will have experienced all kinds of trauma that you don't know anything about.
It's not reserved for the 'troubled' kids. I was a straight A student, middle class family, very polite, plenty of friends, etc and also totally traumatised.