As someone who’s completely self-taught, I started DMing after just a year of playing Pathfinder 1e. I jumped into DMing 5e with barely more than a years worth of playing experience —and I was terrible.
I’d watched one of the early actual plays online, and I remember that after the game, the DM asked their players for feedback. That stuck with me. The show has since been delisted, but that moment shaped how I taught myself: by asking for feedback and really listening to it. At times, I struggled with the same mistake over and over as I grasped for answers in a proverbial darkness.
If there’s a mistake a new DM can make, I’ve made it. I’ve been yelled at by players more times than I can count. I railroaded my first campaign into the ground. I once ran content that wasn’t appropriate for my group. I chased difficulty too hard and caused more than a few TPKs. I went years without being able to keep a stable group. But eventually things started to click.
These days, I do watch some YouTuber (many of the ones mentioned in this thread), but honestly, none of them taught me as much as doing it did. Advice without context is just noise. Even when I knew the basics from being a player, I still had to fail—often multiple times—before I understood how to DM well.
Now, seven years later, I run two full weekly campaigns and have a waiting list of players who want back in. But it wasn't a quick journey. I took several breaks during that time due to burning out for months, from being unable to solve a problem I was running into.
So my advice? Let them try it. And then let them try it again, when they fail.
They will screw up. That’s part of learning. But watching every tutorial and reading every guide won’t prepare someone like actually running the game will. DMing is hard—and in my experience, doing it is the only way to truly learn how to do it well. And it requires a lot of listening and humility.
I hope your 11 year old has the patience and desire to learn how. It really is incredibly rewarding to watch the enjoyment you can bring to so many through a game.