Originally posted by NotUrsula
Gail, you're right; I misspoke. SWA does *list* two (actually, three) fare categories for the younger set: Infant, Child, and the little-known Youth fare.
However, I checked with SWA about how those fare categories are calculated, and was told that in price terms they still are almost never the least expensive alternative, as they are all calculated the same way, as a percentage off the "Refundable Anytime" fare class. The percentage may be up to 50% for children under 2, while it seldom exceeds 20% for older children.
(The percentage varies, based on day/time/route.)
As a practical matter, as long as you are not buying a walk-up fare, it will pretty much always be cheaper on SWA to buy a child an adult fare in a discounted advanced-purchase fare class, rather than the designated special fare based on passenger age.