Junior pricing is half the adult price so that isn't as much of the issue as the fact that no concession seating is available for PL matches. Someone did the maths and worked out between the ST holders, away allocation, supporter club allocations and lack of availability for concessions in all parts of the stadium, you're looking at hardly any seats for junior members.
What they should do (IMO) is allow people to use concession pricing on ticket exchange seats, which are virtually all full price. All they'd do is lose the difference between the ST full price seat and the concession price - something that would happen anyway if they had more concession seats available. That they don't do this just underlines that greed is the motive.