Children under 11 will be able to enjoy free travel on all National Rail services in London from 2 January, the city's mayor Boris Johnson has said.
At the moment children are only allowed free travel when they are accompanied by a paying adult on Tube, Transport for London (TfL) rail, Docklands Light Railway, and London Overground trips.
The mayor said "hundreds of thousands of families" would benefit.
Meanwhile, season tickets will rise by nearly 1% in the new year, TfL said.
In August, Labour chair of the Assembly's Transport Committee Val Shawcross argued that children living south of the Thames were more likely to have to pay for their travel than their north London counterparts.
This is because train companies operating in south London have not offered the same concessions as other transport providers including London Underground.
Boris Johnson said "hundreds of thousands of families" would benefit from January and that it would "take away the fares confusion for so many, opening up wider travel in the capital".
TfL has committed to pay £500,000 a year to the train operating companies to secure the deal.
Lynn Gradwell, director of children's charity Barnardo's in London, said it would bring costs down for families and "make it a little easier for children from poorer backgrounds to experience all that the capital has to offer".
Other fare and transport news announced includes:
- Stratford and a number of adjacent stations, including West Ham, Canning Town and Stratford International (DLR), will move from Zone 3 to the Zones 2/3 boundary
- Travelcard season ticket prices go up by just under 1%, in line with a Conservative manifesto pledge that no regulated National Rail fare should rise by more than inflation
- Single bus fares are frozen, but the daily bus price cap rises by 10p to £4.50
- Off-peak pay-as-you go fares in zone 1 and zones 1-2 increase by 10p