Above the building towers is a crane, with a red light visible at night at the top - perhaps an allusion to a Christmas tree.
An almost identical artwork also appeared a few kilometres away under the multi-storey Centre Point building in Tottenham Court Road, where the two children can be seen looking up at the London skyscraper.
Both images attracted interest from passers-by and generated much speculation on social media about whether Banksy was behind them.
But by 4pm only the Queens Mews artwork had been posted on Banksy’s social media.
In September, the artist took aim at Britain’s crackdown on protesters with a new work outside the Royal Courts of Justice in London, adding fuel to a free-speech row rocking the country.
The artist posted an image of the work, which features a judge wielding a gavel over a protester on the ground holding a blood-splattered placard, on his Instagram page.
The work was later covered by black plastic sheets and two metal barriers.
It appeared after hundreds of people were arrested at a demonstration against a ban on the activist group Palestine Action.
In May this year, one of his paintings, which reimagines Jack Vettriano’s famous The Singing Butler, sold for nearly £4.3 million ($10m) at an auction in London, auction house Sotheby’s said.
-Agence France-Presse