A witness described the dog as being like “a large American Bully type breed” online.
A man has been charged with being in charge of a dangerously out of control dog and the pet has been destroyed.
A neighbour who witnessed the attack told The Sun: “The woman was screaming quite loudly.
“He had his dog on a lead, over the way, the attack had already happened. Next to the Double Tree.
“He (baby) was screaming and had a bite on the leg. The mother was beside herself.
“I ran out thinking if someone needed CPR.
They said: “Thanks again to all who helped. Not trying to scaremonger but do take care if you see those dogs - especially those with children.”
A Met spokesman said: “The child was taken to hospital where their injuries were assessed as not life-threatening.
“The dog and its owner were located by officers.
“A man has been arrested on suspicion of being in charge of a dog dangerously out of control. The dog has been seized and will be taken to kennels.”
A Met task force had previously posted on X, formerly Twitter, that the dog had been destroyed.
Thomas Ackah, 29, of Old Kent Road was charged with being in charge of a dangerously out of control dog.
He is due to appear at Bromley Magistrates’ Court on Tuesday the force said.
They added: “The boy’s injuries have been treated at hospital. They are not life changing or threatening, fortunately. We wish the victim all the best with his recovery and thoughts with his family.”
It comes the week after hundreds of XL Bully owners protested Rishi Sunak’s ban by joining a march in central London.
Crowds amassed in the capital to protest the move, insisting their dogs are completely safe and that only a minority are dangerous.