NRK had a series on puberty that is no-nonsense, straight to the point. It was hosted by a physician. Most of it is on YouTube, and from a very brief look has English subtitles. Warning, it contains full frontal nudity of people at various ages. It is rated for children in Norway, but might be shocking to someone not used to seeing nipples on TV. It should be quite informative. Watch it yourself and decide if you want your son to see it. I have no idea if it is geoblocked.

https://www.youtube.com/watch?v=V0tfIut5oJU

[…] nobody uses SIP…

Say what?

In my part of the world signaling for literally every phone call, be it mobile or fixed, traverses networks and operators using SIP.