Since a guy's cock is a barometer of his health and things can go waaay wrong before we're old enough to make decisions on our own, it's extremely important that parents are able to discuss things openly with thier sons. Besides taking a line drive to the balls, besides getting kicked in the crotch in a soccer game (traumas usually immediately addressed by a coach) things can go wrong that should be dealt with before they become a serious issue.
Since more than 50% of births in the US are now outside of marriage, there are more single moms out there than ever before! So, Ladies, it's important for you to know these things too. You've got, or may have, sons who need to be able to come to you if something is amiss. And you need to be able to ask if everything is behaving normally, without stammering and stuttering and without embarrassing your son. And I know you ladies like to talk trash about us guys and our dicks when you get together with your girlfriends... If you've got a few BFF's who are single moms with sons, talk! Make sure they know and understand the importance of this stuff.
And, Dad, you should be even more capable of that than Mom! You've got a cock, you've got balls; you know what they should or shouldn't be doing. It hasn't been that long since you've gone through it - or have you forgotten how your body changed, how your life changed, when you started popping boners and spewing cum?
If you can't bring yourself to address these issues, you need to haul your son(s) off to a doctor at age 13, or so, and tell him you want a complete check-up on the package. Are things growing and maturing properly? Micro-penis or hypogonadism can be found and treated. Make sure the doctor will ask if they're experiencing good solid boners; the Bone-ometer is just as important at this age as any other. He can also teach him how to do a good ball check. Testicular cancer strikes mostly between the ages of 15 and 40, which means it could hit a guy younger than 15, too!
There are plenty of other issues our not-quite-mature packages can face, as well. An unusual dark spot could be nothing more than than that - just a skin discoloration - or not. Rough, red spots along the shaft or on the head could be nothing more than balinitis (dry skin of the penis), or they could be pre-cancerous or cancerous lesions. Not cleaning under the foreskin several times a day (especially as a teen oozing pre-cum almost constantly) can result in pustules growing along the coronal ridge.
Make sure your son(s) know how to listen to their dicks.
Make sure you listen to your own.