Hartington,
I assure you that I paid the same price for my ticket as I did for SD juniors ticket, and this is the case for all the airlines I have flown with or checked prices for.....
Regards, SD.
PS. If you are talking about a child under 2, who is to sit on the parents lap, then that could be different. But if you want a separate seat for your child, then you definitely pay for it, I know from experience!!!