The older kids are often the easy source for the younger kids. At 8 I had already seen a Playboy and knew kids who had seen harder stuff. I could have easily gotten a teenager to get me cigarettes (and drugs, but I didn’t know what those were really). I had also already tasted alcohol. Any of this I could have stolen from any number of places.
At 16 it was easier, but at 8 it wasn’t hard.
There’s a difference between “saw a playboy once” and having regular or semi regular access to it.
Same goes for alcohol and cigarettes.
If you had regular access to those things you had parents who didn’t care.
It’s also not about kids on the margin. The vast majority of 8 year olds have not tried alcohol, drugs, or cigarettes.