A man who vandalised Facebook tribute sites for two dead children has been jailed.

Self-confessed "troll" Bradley Paul Hampson, 29, of Tarragindi in Brisbane's south, posted pictures of penises and wrote offensive messages on the two sites in February last year.

On one Facebook tribute site for the 12-year-old boy, he wrote "woot I'm dead" across an image of the dead child.

He also morphed a photo of the boy's face inside a woodchipper and made it appear blood was coming from the machine.

On another, he wrote sexually explicit comments implying he was responsible for raping and killing the eight-year-old girl.