The problem, at least in some countries, is that the laws regarding targeting children and teenagers are VERY strict, to the point where it almost doesn't make

The problem, at least in some countries, is that the laws regarding targeting children and teenagers are VERY strict, to the point where it almost doesn't make sense to do it. By having an "unknown" category, you could argue that you had no way of knowing that you where targeting children, so you can't be responsible. The other party could also easily argue that they put those under 18 in that group to protect their privacy and age. If you however DO know that these are primarily children and teenagers, then you have to follow the rather strict laws. In Denmark for instance, that means that you cannot encourage purchasing or even advertise certain products. Take the stupid product that is Prime (the drink), health professionals argues that it's harmful to children, but their are also the only ones who really buy it in any meaningful volume. If you knew that you where targeting Prime ads to those under 16 in Denmark, you would be breaking the law. If advertising companies where to follow the laws online (technically they have to, but tries to avoid it), you could effectively reduce the number of ads you see on social media by stating that you're only 16, because you couldn't be targeted in the same way.