That's because you've effectively transferred it to someone else (an adult) which isn't allowed.
I sat on that bloomin' PSL leaflet for ages, umming and ahhhing. Hope they do relaunch it.
The other problem is that if you decide that there are more than 6 games that your under 10 can't attend, you can't change their seat ticket to a full paying adult in the name of your mate, as season tickets are non-transferable.
So you either have to have an empty seat for those games, or let...