Seven children are being treated for TB after the outbreak in Westminster, according to the Health Protection Agency.
The cluster of cases follows the diagnosis of TB in an adult with links to the nursery in July.
A further 26 children who came into contact with the adult show no signs of TB but are receiving a shorter course of antibiotics.
A second adult, who works at the nursery, has received a full course of treatment for TB, and is currently off work. Six other adult staff were given shorter treatments.
The HPA’s London director Dr Brian McCloskey said the original case may have been particularly infectious because they had been suffering symptoms for eight months prior to diagnosis.
Some tests are still being examined out due to the difficulty of diagnosing TB in children.