Most flights I know charge full or almost full prices after 2 years of age. Pretty awful I agree, but it seems to be their policy.

Most of the charter airlines are adopting the lowcost model for pricing air tickets where its the same for adults and kids.

I think Excel offer child prices.

Unfortunately, although it seems a bit rotten to pay full price for 3 year olds on flights, they take up a seat just as any adult would. So from the point of view of the airline, there is no reason to offer them any reduction.

If you look at it another way, the cost to operate the aircraft is the same regardless of who the passengers are, so the easiest way to calculate the individual cost is to divide the total cost by the number of seats on board. If the cost for children is then lower, then the airline has to make up the difference by charging adults more, which is then unfair for those travelling without children. So I think most airlines have come to the conclusion that not only is it easier for them to unify the cost of seats, it is also fairer (expect for families, of course!).