Most young boys will frequently touch or play with their penis. This is a normal part of their development and how they learn about their body. Once the foreskin .
It could be because young boys are more likely to be in the chigger The redundant skin just proximal to the glans penis has great capacity to swell with this.
You see it in movies all the time. Some guy gets hit right in the privates. Yow! If you're a boy, you probably already know your penis and scrotum are sensitive.