Scotland Yard yesterday arrested more than 100 people on suspicion of various offences, including 50 related to drugs, 20 for possession of offensive weapons, four for actual bodily harm, two for grievous bodily harm, one for theft and one for public disorder.
They also seized illegal laughing gas canisters from some of the carnival revellers.
"Metropolitan Police licensing officers working at this weekend's Notting Hill Carnival have seized over 150 canisters of nitrous oxide... The canisters have a street value of over 2,000 pounds," a Metropolitan Police statement said.
The child is in hospital and remains critical.
It is celebrated over Sunday and Monday, which is celebrated as a "Summer Bank Holiday" in the UK, and is believed to attract around 1 million people as West Indies origin Britons come together for the celebrations.
Met Police mounted heavy police presence for this year's festivities and have also introduced advanced security measures such as a facial recognition system.