As others have said, the Ticket Exchange is your best bet, but you can probably forget about junior tickets (are they even available on the Exchange?).
They are, but like hens teeth.
As a season ticket holder it doesn't affect me, but one thing I'd like to see is that the queue is not opened until exactly 10:00.
This is a slightly odd one. They seem to open the queue at pretty random times at the moment - anytime from 8:30 to 9:30.