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.

The 28-year-old's contract with Korona Kielce in his homeland had expired and Grzelak has also played for Wisla Plock, Dolcan Zabki and Podbeskidzie Bielsko-Biala.
He becomes head coach Ian Cathro's third summer signing.
"For me, it's important that this club will be my home and I'm really excited to be here," Grzelak told the Hearts website.
"I've had a really good impression from everybody that I've met here so far, and I've been told that the fans are fantastic.
"When I knew that I could come here, then I was very happy to come.
"My good features are that I am a strong player, who likes to tackle, and I prepare myself well for the physical side of the game. But I am also very calm on the ball.
"I can play in defence, both in the centre and on the left, and I can also play in the centre of midfield."
Hearts, fifth in last season's top flight, have already signed defender Christophe Berra and forward Cole Stockton so far this summer.
Find all the latest football transfers on our dedicated page.

Wilson's side were demolished by 101 runs against Hampshire on Tuesday.
But Wilson said they were not too worried about a one-off defeat and instead took heart from their form throughout the group stage.
"It's disappointing to go out one step away from Finals Day and we'll come back next year," said Wilson.
"We will take pride from the brand of cricket we've played throughout the competition."
Derbyshire were the surprise package of this season's T20 Blast, finishing second in the North Group having reached the quarter-finals only once before.
"We were all desperate to get over the line and get down to Birmingham," Wilson told BBC Radio Derby.
"We won't accept that a quarter-final is good enough.
"But, moving forward, it could be an exciting time for us and the challenge will be to go one step further."
A disc jockey has been jailed for eight months for stealing money from a children's cancer charity linked to the Oscar Knox appeal.
[NEXT_CONCEPT]
Polish defender Rafal Grzelak has joined Hearts on a two-year deal.
[NEXT_CONCEPT]
Derbyshire captain Gary Wilson has said his side will be back in contention for T20 Finals Day next season after their quarter-final defeat to Hampshire.