The vast majority of ads I see on YT are scams or over-hyped products that can't work as advertised (damn physics). I haven't looked, but it must be super cheap to advertise on their platform. Are they truly marketing at kids? Any more than children's TV programming is loaded with ads for Chocolate Frosted Sugar Bombs, expensive theme parks and over-priced toys?
Ultimately, parents are responsible for their children and need to monitor their children's activities. If online portals are exploiting them, maybe it's time to learn how to use those parental lockouts. When I was growing up we had to ask if we could watch TV and tell dad what we wanted to watch. It was usually "yes" and Saturday morning cartoons were a given, but there could also be a "no" if there were still chores or homework to do. Reading was encouraged and there were plenty of books in the house along with Tinker Toys, Lincoln Logs, Mechano, etc. between my friend next door and I, we must have had 20kgs of legos.