Since 1966, The Notting Hill Carnival comes every August Bank holiday with its sense of Rio/ Carribean flavour on the streets of London. There is roughly 20 miles of vibrant kaleidospoic costumes surrounded by 40 sound blasters with over a hundred Carribean food stalls.
The Sunday is Kids day where the Main Parade is on Monday with the festivities starting at Great Western road ending at Ladbroke Grove at about 7pm.
For more info, have a look at http://www.thenottinghillcarnival.com/.