Coca-cola was recently found guilty of this in the "food industry self governing organ" in Norway [1]. This is where complaints go first and if Coca-cola continues it can result in fines and whatnot.
They were using people from youtube channels that primarily makes videos for children in their own youtube channel videos.
[1] https://translate.google.com/translate?sl=no&tl=en&u=https%3...
From my now very vague memory of childhood TV, most ads for toys and games came in the evening news and soaps slots. When the adults were around too. Junk food was still OK, so kid's tv ads were for comics, and sweets, and sugar, oops I mean cereal: Sugar Puffs, Ricicles, Frosties etc.
I think it's a big mistake our regs on advertising toys to children have faded over the years. It's been shown time and again kids 12 and under can't understand commercial intent by ad industry research. So the real age may be higher.
If I post a video of my game on Reddit, am I marketing to children? There are a lot of children there, but it isn't a childrens' website. Does it matter if my game is strategy-/turn-based or animated with cute graphics?
Identifying demographics and targeting the marketing to them is the bread and butter of modern advertising. The entire justification for Google's and Facebook's mass consumer surveillance is to offer corporations more targeted advertising.
There are gray areas but if you're marketing to children, you know you're marketing to children.
For cases like this it's much easier to evaluate it case by case.