Gary Neville, from Cupar Way, Belfast, raised Â£930 at a charity fundraising music night he organised last year.
He was prosecuted for failing to give the cash to the Neuroblastoma Children's Cancer charity.
Oscar Knox, a five-year-old boy from Glengormley, County Antrim, died from the rare and aggressive cancer in May.
The child's story captured the attention of the Northern Ireland public as each step of his cancer battle was followed on social networking sites.
Neville's solicitor told the court his 33-year-old client was "utterly ashamed" of his actions.
The lawyer said he had got into financial difficulty and was under threat of eviction from his home.
He added that Neville had written a letter of apology to the the Knox family.
Sentencing him to eight months in prison, the judge said it was absolutely shocking he would use circumstances such as a child's death for financial gain.
Neville, who is currently in prison for other offences, was told his term will run concurrently with his sentence.
The Knox family set up the Oscar Knox Appeal and still use the networking sites to raise awareness and funds for organisations helping children with Neuroblastoma.
A disc jockey has been jailed for eight months for stealing money from a children's cancer charity linked to the Oscar Knox appeal.