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...