Tom Piggott, aged 21 and of Maesowen, Welshpool, was found guilty of two counts of raping a child, three counts of sexual assault on a child, two counts of inciting a child to take part in a sexual act, and three counts of making indecent images of children.
Piggott, a former Oswestry Otters swimmer and Swansea University student, was aiming for a place at the Tokyo Paralympic Games in the S10, SB9 and SM10 disability swimming classes but is now facing prison after being convicted at Mold Crown Court.
He had denied the offences but it took a jury less than half an hour to return a guilty verdict on all 10 counts following a five-day trial.
Officers found 141 videos, 58 of which are in the most serious category, and 29 indecent images, six of which are in the most serious category, on electronic devices seized from Piggott’s home.
Investigating officer Detective Constable Steve Williams, of Dyfed Powys Police, described the images as some of the worst he had ever seen and praised Piggott's victims for their bravery in coming forward and telling the truth.
He also condemned former Welshpool High School and Shrewsbury Sixth Form College student Piggott's "incredible arrogance" in attempting to lie his way out of trouble.
“This investigation has been a massive undertaking for all involved,” Det Con Williams said.
“From the investigating team, to the digital media investigators, it has been an incredible amount of work, but we’re satisfied it has been worth the effort to get justice for these young victims.
“None of this would have been possible without their strength and bravery in coming forward.
“It is their willingness to tell the truth about what Piggott did to them that has meant he has been convicted.
“Piggott showed incredible arrogance in trying to lie his way out of the situation he found himself in as a result of his terrible actions. But the evidence proved too strong."
Det Con Williams added: “Some of the images we found on his devices were among the worst I have seen in a long career investigating crimes such as his.”
Piggott was remanded in custody to be sentenced at Mold Crown Court on September 13.
Anyone from the Dyfed-Powys Police area who has been affected by crimes such as these, even if they haven't reported to police, can contact the Goleudy victim and witness service on goleudyvictimandwitnessservice.org.uk