CHICAGO (AFP) - Two brothers who belong to a New Orleans gang were charged with opening fire at a Mother's Day parade in New Orleans where 20 people were shot, police said on Thursday.

Sunday's shooting at a crowded parade filled with families shocked the Big Easy, which is struggling to overcome what mayor Mitch Landrieu described as "the relentless drumbeat of violence" on its streets.

Most of the victims escaped with non-life threatening injuries after they were grazed by the bullets sprayed into the crowd, but two 10-year-old children were among those shot.

"We are going to do what we have to do to protect our culture and our great city," Mr Landrieu vowed at a press conference. "We will not bow down."

Akein Scott, 19, was booked into custody at about 3am on Thursday on 20 counts of attempted murder. His brother Shawn Scott, 24, was arrested later on Thursday on the same charges, police said.

Four other people were charged with obstruction of justice and "accessory after the fact" for helping Akein Scott hide from police even though they knew he was the subject of a massive manhunt.

"We believe Shaun and his brother Akein are associated with the gang Frenchman-Derbigny Boys," New Orleans police chief Ronal Serpas said.

"Shawn has a lengthy record and has demonstrated his contempt for the people of New Orleans," he added.

Shawn Scott was on probation after serving time on drug charges and warrants were already out for his arrest on unrelated weapons and drug charges.

Police found cocaine and heroin when they arrested him.

Akein Scott was out of jail on a US$15,000 (S$18,700) bond at the time of the shooting after pleading not guilty to charges of illegally carrying a weapon last month.

He had also been charged with resisting arrest and heroin possession, according to the Orleans parish sheriff's department.

He had previously been arrested last year for possession of a stolen weapon, but the charges appear to have been dropped.