What's the crack with the juvenile ticket wheeze?

The offer to get cut price tickets yesterday for early bird arrivals at £20 may have put a few bums on seats. But a bunch of guys in the pub after the match reckoned as well as two of them buying these discounted tickets, they also bought juvenile tickets at £15 and simply scanned them as no stewards are involved in the checking. Is this possible and whereabouts in the ground are these tickets allocated?