Ernie Moon was born in Walford General Hospital on the 8th August 2014 and he is the son of Alfie Moon and Kat Moon, as well as being the twin brother of Bert, younger half-brother of Tommy and older half-brother of Cherry.
Bert was born on 8 August 2014, though the first baby to be born is not breathing and has to be resuscitated. During the pregnancy the babies are nicknamed "Bert Moon and Ernie Moon" after the Muppets, and although Kat insists the names are temporary, Alfie eventually wins her round and they decide to register them as Albert and Ernest after they are unable to come up with alternative names. When the twins are one month old, their home is burned down by Alfie as part of an insurance scam; this results in Kat being badly burned and spending a month apart from the twins to recuperate in hospital.
Their parents later separate when the twins are four months old after Kat finds out Alfie was responsible for the fire and as a result they move in with Kat's cousin Stacey Branning, her daughter, Lily Branning, and their great grandmother Mo Harris. Their parents reunite and after they win the lottery Kat and Alfie relocate to Spain with the twins and their older half-brother Tommy Moon. They return briefly with the family in December 2015 and January 2016. In 2018, Kat returns from Spain and though she misses the children, she ignores Alfie's calls. It is revealed that Ernie was scalded by hot water while Kat was having an affair, and Alfie blamed Kat and sent her back to England, but did not know about the affair at the time.