He was found guilty on 22 counts, including rape sexual assault and child neglect, after an eight day trial, police said.
The court heard how Long took advantage of his access to the five children, all aged between six and 15 at the time and living at different addresses in Eastbourne. He treated the boys with cruelty and subjected the girls to regular series of sexual offences, police said.
It was only when one of the victims disclosed for the first time what happened to her and the others that police were able to carry out a full investigation, a police spokesperson said.
Detective sergeant David Gibbs, of the East Sussex Safeguarding Investigations Unit said: Long was a systematic offender against vulnerable young children, using his access to them for his own heartless gratification.
"We admire the readiness of these victims, each of whom experienced real emotional as well physical trauma, to give evidence. This, together with evidence we put together, with great assistance from PC Joanne Fox who worked closely to support the victims, Simon Milloy in our Witness Care team, and John Cousins from our Statement Taking team, was clearly a major factor in the outcome of the case.
"Although Long pleaded not guilty to all charges, such was the strength of the evidence that the jury returned unanimous guilty verdicts on all 22 counts barely two hours after retiring."
"If you, or anyone you know, is subjected to abuse of this kind, do not suffer in silence. Please contact us at any time, on 101 or online and arrange to talk in confidence to experienced investigators."