A man has been jailed for plastering child pornography over Facebook sites set up to pay tribute to two dead schoolchildren.

Bradley Paul Hampson, 29, posted offensive comments and pornographic images on social networking pages honouring a 12-year-old boy and an eight-year-old girl.

The boy died in February last year after being stabbed in the chest during a schoolyard fight.

The girl's body was found in a drain near her family home at Bundaberg in the same month.

More than 9000 people joined the tribute pages, posting messages of condolence.

However Hampson instead posted digitally altered images of the children along with vulgar messages.

He pleaded guilty in the Brisbane District Court on Friday to one count each of distributing child exploitation material and possessing child exploitation material, and two counts of using a carriage service to menace, harass or cause offence.

The court was told Hampson was arrested in June last year after police carried out a search warrant on his home at Tarragindi, in Brisbane's south.

They seized computer equipment which contained altered images of the boy and the girl.

The hard drive also contained offensive images he had created of Madeleine McCann, who disappeared while holidaying with her family in Portugal in 2007, and James Bulger, a two-year-old boy who was murdered in England in 1993.

Hampson claimed he defaced the websites because he had been previously harassed online.

He was sentenced to three years' jail, but will be released after serving 12 months.

He has already served more than seven months in pre-sentence custody