MONTGOMERY, Ala. — About 2,000 children marched arm-in-arm Thursday, singing "We Shall Overcome" as this once-segregated city marked the 50th anniversary of Rosa Parks' refusal to give up her bus seat to a white man.

"Because of the action of Rosa Parks we have witnessed — here in Montgomery, in the state of Alabama, all across the South — unbelievable changes," Rep. John Lewis, D-Ga., said after laying a wreath at the site where Parks was arrested on Dec. 1, 1955.

The children, both black and white, marched eight blocks from the downtown site to the Capitol, singing anthems of the civil rights era and chanting "Thank you, Rosa Parks."

The march was one of many events in Montgomery and elsewhere remembering Parks' stand and the 381-day bus boycott that followed. She died Oct. 24 at age 92 in Detroit.

In Washington, President Bush signed a bill directing that a statue of Parks go up in the Capitol's Statuary Hall, making her the first black woman to be represented there.

In Montgomery, civil rights leaders joined the children for a program at the Alabama Capitol, where 12-year-old Courtney Meadows urged young people to stand up for what is right, just as Parks did.

"I believe it was one of Mrs. Rosa Parks' greatest dreams and today she is looking down on us. It's time to take action," he said after the program.

The program included readings from speeches by the Rev. Martin Luther King Jr., who gained renown leading the boycott, and from fliers passed out by hand in 1955 urging blacks not to ride the buses.

"Look back, but march forward," boycott veteran Johnnie Carr urged the crowd.

Elijah Taylor, 12, said he joined the children's parade "to give tribute to all those people in Montgomery who walked during the bus boycott," as well as Parks.

The boycott, which hurt the city financially and drew the nation's attention to the emerging movement for racial equality, ended Dec. 21, 1956, after the Supreme Court upheld a federal court ruling that outlawed racial segregation on city buses.

All buses in Montgomery paid tribute to Parks by leaving a seat empty with a display commemorating her act of defiance.

In New York, empty seats were marked with posters of her reading, "It All Started on a Bus," and bus drivers were keeping headlights on all day.

In Philadelphia, middle school students planned to write comments about Parks on posters on the outside of a bus that would be put into regular service.

Bus tributes had also been arranged in Boston, Cleveland, Newark, N.J., and Washington, D.C.

In Detroit, a federal building on Detroit's east side was being renamed for Parks in an afternoon ceremony. The resolution renaming the building was signed into law by President Bush on Nov. 11.