Long and enthusiastic cries of "Yesssss" rang out as Derek Riley asked from the stage if anyone in the thigh-high crowd watched "Sesame Street."

To the few who responded no, he playfully replied, "Yeah, y'all do."

Having broken the ice, Riley soon had reggae and go-go beats coming from his keyboard, coaching the youngsters through the hokeypokey and such lyrics as "knick-knack, paddy whack, give a dog a bone, this old man came rolling home."

Riley allowed them to do shout-outs to the people from their neighborhood and, reminiscent of adult parties, had the young and the old throwing their hands in the air, waving them like they just didn't care. It's all part of his traveling road show of nursery rhymes and children's songs infused with a hip-hop flair.

At this recent event, the kickoff of the D.C. Department of Recreation summer program in Anacostia Park, hundreds of children from across the city were arriving in busloads to play games, swim, eat and listen to music. Riley's job was to jump-start things.

"He gets the kids invigorated," said Yvette Davis, outreach librarian for the D.C. Public Library system, which has hired Riley to visit dozens of libraries this summer.

Riley, 36, seems to be having as much fun as the children, something he acknowledges at his shows. "I'm about the biggest kid you'll ever see," he told the crowd.

At 6 feet 2 inches tall, Riley cuts an imposing figure. Children, he said, come up to him all the time and tell him he's fat. "They don't mean anything by it," he said. "Kids are just honest."

Riley knows. He has more than a decade of experience as an early-childhood educator. And since he's been able to walk, he's been alongside his mother, Shirley Riley, as she supervised activities at the Nursery Hut Child Education Center in Northeast, which she founded in 1964. As her own children grew older, they helped out at the center. After trying construction work, Derek Riley joined her there, getting his child-care teaching certificate in 1993.

Always a fan of music, he started a music program for the center's children.

"All the kids would say 'yea' when he pulled out that keyboard," said Shirley Riley, 64, who closed the center last year. "The little infants would move their heads in the cribs. When he would play, we could never get the parents to go home on time. The center closed at 6 p.m., and some parents would not leave until after 7 p.m."

Riley's stage name, Mr. Derby, comes from a nickname his father gave him as a child, with the "Mr." added by parents who reminded their kids not to call adults by their first names without an honorific. The character has an outlandish English accent and typically dresses in a khaki vest and pants with a signature white derby. He's been performing regularly for a little more than a year.

In 1998, a parent from the center brought in some equipment one day and recorded a live album with Riley called "Mr. Derby's Nursery Jams Vol. I." Through word of mouth and events, Riley said, he has sold about 2,200 copies. He's now working on additional music and hopes to have another album soon. And since his mother closed her center, he has decided to spend more time on his music. He has more than 50 events planned this summer, most through the library.

Shirley Riley said her son's interest in music began when he was a toddler. He would pull pots out of a cabinet to bang and broke the arm on the family record player a few times before learning to use it properly, she said. By the time he was 12, he was playing small gigs for the family. But once the boy finished school, his father, a plaster contractor, lured him into construction. Riley ended up returning to the day care, however.

And that led him back to music.

Because Riley sings most of the nursery rhymes to reggae and go-go beats, he's also a hit with adults, and even some teenagers, who tend to be apprehensive about appearing to enjoy the show too much. But he's careful to keep the show G-rated because children are bombarded with so many negative and vulgar images, he said. While working at the day-care center, Riley said, he became distressed by 3-, 4- and 5-year-olds regularly using profanity.

"I wanted to give them music they could dance to and it still be children's music," he said.

One of his biggest fans is his 2-year-old daughter, Ashley, who shoos the other children away from the keyboard when her father is playing, Shirley Riley said.

When his daughter's not around, however, Riley can turn his full attention to other youngsters. After bouncing and singing along with Riley for an hour, 9-year-old Deara Adams, who attends Simon Elementary School in Southeast, summed up the performance this way: "He did some good music."

Derek Riley, whose stage name is Mr. Derby, revs up youths at a Department of Recreation event in Anacostia Park.