I know this is HN, but I have a hard time believing this. Somehow feels like nostalgic self-congratulatory boasting.
Honestly curious, what does it mean for a 5-year-old to be programming seriously?
I also branched out from just making games, and started writing programs to solve things for me, for example, a budgeting program.
At 6 maybe you type that huge program that creates a sprite ball that bounces across the screen. By 7 you are drawing out sprites on grid paper and making that bouncing ball different pictures.
It took me until later in highschool to understand things but typing and modifying is programming. My variables for loops were always lili,lolo,lala,lulu,p naming them there purpose seemed foreign.
Not sure if I'd be able to pull off the same at 5, but it doesn't strike me as utterly impossible. Also, the GP didn't say what was the result of his "serious coding" - could be nothing (working) at all until much later.
It's not about career prospects. It's about joy and about learning a way to structured thoughts which few other activities can provide. A computer can't be argued with or tricked. It executes instructions. You can't beg it to be nice, you have to actually fix the bug. It won't betray you either. This very strict cause-and-effect property is a very important lesson that too few members of society have understood.
You may wish to show your kids something like Scratch or even just drawing pictures with Python's turtle library, just to get a feel for their interest level. If they figured out how to install games and stuff on their own, they are good candidates for programming, provided they are interested. Most importantly, you cannot rush it. They will become interested in programming (or anything else) if and when they are ready. Any age is a good age to get started. I have much respect for folks who discover programming during middle age or older.
Oh, and like the other commenter said... worry about their career prospects later. Right now, for them it's about having fun.