FORT WORTH, Texas — It's getting more expensive to fly these days — even for babies.

Several major airlines have quietly dropped discounts for children younger than 2 in recent weeks. Although infants and tots can still fly for free on Mom or Dad's lap, parents must pay the adult fare if they want a seat for the little one.

"We found out that this was very rarely used, frankly," said Tim Wagner, spokesman for Fort Worth-based American Airlines. "Most people just carry their young children in their lap."

He said the airline stopped offering the discount Jan. 13.

The program allowed parents to buy a seat for 50 percent off if the child was younger than 2.

Delta Air Lines, United Airlines, Alaska Airlines and others also have phased out similar baby discounts.

Continental Airlines still offers some children's fares, but not in all markets. Southwest offers infant fares for parents who wish to use an FAA-approved child airplane seat.

"If they want to occupy a seat, they'll pay the lowest applicable fare," said Betsy Talton, a spokeswoman for Delta, which ended its baby savings Dec. 26. "And we still have the option that they can fly for free in an adult's lap."

In the past, the discount for pint-sized passengers brought the airlines more revenue, because parents often opted to simply carry the child rather than pay the full price.

But today, empty seats have become scarce on the nation's airlines, thanks to cuts in capacity coupled with increased demand.

That means a baby could be taking up a seat at half price that might otherwise go to an adult paying full fare.

"This is entirely driven by demand," said Stuart Klaskin, an airline consultant with Klaskin, Kushner & Co. in Coral Gables, Fla. "If the airlines have the opportunity to sell the seat to someone at full price, they're going to jump at that."

Airlines have been slashing other discounts as well. Delta and US Airways reduced so-called bereavement fares for passengers traveling to funerals of close relatives.

Meanwhile, they've implemented charges and fees for many services, such as curbside check-in and in-flight food.

Fares have been rising steadily for more than a year, buoyed by high fuel costs and pricing discipline among the major carriers.

Airline officials also point out that the discount typically wasn't applicable on the cheapest nonrefundable fares. So for families planning in advance, the cheapest published fare might be less expensive than the children's fare.

"Our lowest fares were usually cheaper than the discounts," said American spokesman Tim Wagner.

Airlines continue to recommend that parents buy a baby a seat, even at full price. American's Internet site, for example, states that "for the safety of your child, American recommends purchasing a seat and using an approved child safety seat."

Klaskin agrees.

"We have to stow and secure everything during takeoff except little children," he said. "From a safety perspective, that's never made much sense to me."