My first impression is that this is a particularly stupid idea. It will probably result in lot of kids not seeing the number because they're a little too short or a little too tall for their age.
For one, there is no "too short" for this particular type of display. It's an under-over type of thing.
For two, they're explicitly taking the 'average height of a 10 year old' for this. You would write off the entire ad as pointless because, as implied by the very definition of "average", 50% of 10 year olds and a smaller percentage of each age below 10 would be unable to see it?
Talk about throwing the baby out with the bathwater...
I think the only cutoff is "lower bound of the height a potentially abusive adult would see it at", and retroactively went back and said "okay this height is average for a 10 year old".
According to what I find from a quick google, average height for a 10-year-old is about 4.5", with it starting to spike up dramatically at the age of 12-13 (from ~50 to ~60"). Without knowing the actual height they set this for, though, it's impossible to say how many kids they would or would not get with this kind of advertising.
It seems to be a novel approach, certainly worth the experimentation. Calling it stupid is going far overboard without intimate knowledge of their expectations and motivations.
