Whenever Kailey Dean heads to the supermarket with her mom, she has one thing in mind: climbing into her miniature race car and steering her way down the aisles. If mom should drag the toddler to a store that hasn't caught on to the kiddie-race-car trend, she could be setting herself up for an ugly shopping experience.

"If those carts are not available, my daughter won't get in," said Mari Dean of Fairfax City. "She gets very unhappy."

The plastic race cars, attached to the fronts of standard-size shopping carts, represent the latest twist in America's infatuation with entertaining its tykes at every turn. At supermarkets across the country, kids now drive their cars, push their own pint-size shopping carts, lose themselves in computer games and gawk at dancing bananas. The distractions allow parents to shop in peace and supermarkets to ring up heftier sales than they might from exasperated parents.

For the most part, supermarkets are responding late to shifting demographics: moms who work, dads who shop and single parents who have no choice but to bring the kids along. With schedules becoming more hectic, bringing the kids helps ease parents' anxiety about diminished face time with their children. Supermarkets have been so preoccupied with growth and mergers in recent years, however, that they have virtually ignored customer service. Now, they see it as one of the few ways to differentiate themselves.

The kiddie cars are showing up at some Giant, Safeway and Superfresh stores, and at the Chevy Chase Supermarket -- but not always to acclaim. A full-size shopping cart with a plastic racer jutting from the front easily becomes an aisle-hog. Fearful of traffic jams, grocers have had to limit the number of carts in each store.

Still, when Wegmans Food Markets Inc. opens its first store in the D.C. area next year, in Sterling, kids will not be deprived of the chance to lumber down the aisles in their race cars. The company says the carts have been a huge hit in every store that offers them. Grocers love the big combo carts because when mom isn't reaching out to pacify a mewling child, she can use her free hand to add another jar of pickle relish to the basket.

"If your shopping experience with your kids is calm and relaxed, you're probably going to be interested in spending more," said Kevin Stickles, manager of Wegmans' Bethlehem, Pa., store.

Parents tend to spend 10 to 40 percent more if the kids are with them and in a relatively good mood, said Greg Kahn, founder and chief executive of Kahn Research Group LLC in Charlotte, which does market analysis for retailers. And the number goes even higher when dad does the shopping.

Impulsive children play an important role in supermarket sales. "Grocery stores are designed to be impulse centers," Kahn said. "They're designed for kids. That's why you always see a kid tugging at someone's arm saying 'Buy this.' "

So stores are pushing hard to get parents to show up with their young ones. At Stew Leonard's, a specialty market in Connecticut and New York that pioneered the kid-friendly environment, children are captivated by costumed characters called Daphne the Duck or Wow the Cow who wander the aisles. If the tykes tire of Daphne and Wow, mechanical bananas and celery sticks take over, singing and dancing on suspended stages. When the bill hits $100, the cash register moos.

The family-owned company made it into the 1992 Guinness Book of World Records for having "the greatest sales per unit area of any single food store" in the United States. It also could be said that it has spawned the current rash of imitators.

Stew Leonard's, which has only a few stores, offers more lavish kids' entertainment than the giant chains. But the latter are starting to go beyond coin-operated rides and free cookie clubs.

At Giant Eagle, Kroger and Wegmans, for instance, kids can hang out at the stores' supervised play areas and play computer games or watch videos while their parents shop. In the Washington region, Giant Eagle is considering building a play center for kids ages 3 to 9 at its Frederick, Md., store, possibly this spring.

That supermarkets must entertain children at all suggests a parental inadequacy that some may be loath to admit, said William Doherty, a family social science professor at the University of Minnesota and author of "Take Back Your Kids: Confident Parenting in Turbulent Times." "It's part of an overall trend of parents feeling incompetent in managing their children's behavior in public," he said.

The evolution of the grocery business also feeds the need to occupy the kids. These days, a large chain store has 30,000 items on display, requiring some concentration on the part of a shopper. A parent distracted by an unhappy child will spend less time combing the shelves and is likely to leave the store with fewer items. In the 1950s, a shopper found only 5,000 items at the typical supermarket, according to Raymond R. Burke, a business administration professor at Indiana University's Kelley School of Business.

"Whatever retailers can do to help them sort through the tremendous amount of clutter and manage their time would be beneficial," Burke said.

Whatever strides supermarkets have made catering to parents and kids, they still have a long way to go. Many in-store bathrooms are not child-friendly. And it's the rare grocery that makes it easy for mom or dad in the parking lot. Parking spots for pregnant women are tough to find. Then there's the issue of lugging the super-size diaper boxes, the groceries, the child seat and the toddler to the car.

The supermarkets know they can't beat Wal-Mart Stores Inc., the largest grocery retailer in the world, on prices, said Richard J. George, author of "Twenty-One Trends in Food Marketing for the 21st Century." So they're focusing on customer service, which explains the rising popularity of kiddie carts.

"Now it's the cost of doing business, because pretty soon every retailer is going to have a few of them," George said.

That could present its own problems, Doherty said.

"I predict that parents are going to feel entitled to them pretty soon," he said. "They will feel their child is being deprived if they don't get one."

Staff researcher Richard S. Drezen contributed to this report.

Liz Wilson and her son Matthew, 9, put groceries from the Chevy Chase Supermarket into Matthew's kid-size cart.Mariela Oliva, left, and Chaska Hansen, both 10, pluck lollipops from a bin at the Chevy Chase Supermarket, one of the stores trying to appease kids.