The rush-hour death shocked Belgium.
The murdered boy's parents held hands as they walked at the heart of the procession.
They had requested a silent march without banners or signs of political affiliation.
Fears of racial tension have been high as the killers appear from the CCTV footage to be of North African origin but his mother appealed for calm.
"Don't ask me to hate all Arabs," she said in an interview with Belgian newspaper La Derniere Heure.
"The youths that killed my son are thugs but don't generalise."
Some Muslim religious leaders in Brussels called for people to turn in the suspects if they knew them.
