"I will fight, even for the rest of my life, to ensure [he] gets what he deserves... he should never get out of jail, at least to ensure the safety of other boys and girls."
She said the family was still waiting for medical results to confirm her son was not HIV positive.
She said he was also at risk of contracting hepatitis C, an infectious blood-borne disease affecting the liver.
A juvenile court in Dubai is trying a third suspect, aged 17 in the same case. His trial is due to resume on December 25.
One of the defence lawyers said the victim had fabricated his story and that "he had agreed to the sex act with the three men".
Hussein al-Jaziri, the victim's lawyer, said he would appeal and demand the maximum penalty within the next two weeks.
"Justice is done as they were declared guilty... but the term itself, it is not enough," al-Jaziri said.
"The case has not ended yet. There is an appeal, there is a higher court and this case will develop further."
Those convicted of sexual assault can face the death penalty or a life sentence.
The boy returned to Switzerland last month after testifying.
He told the closed court session that he and a friend were tricked into getting into a car in July by the youngest suspect, an acquaintance who offered to drive them home from a shopping mall where they had been playing videogames.
They then took the boys to an isolated spot, raped the French boy and dropped off both of them near a Dubai hotel, the boy said in testimony recounted by his mother.
"[My son] is going to be really disappointed believe me because he wants a big justice," Robert said.
"We will be very lucky if turns out he does not have Aids... but we will appeal regardless of the medical results," she said.