Robert Newsham, 78, was found guilty at Exeter Crown Court of two counts of indecently assaulting the 11 year old.
Judge Phillip Wassall warned he faced "a substantial" jail term.
Newsham previously admitted 10 charges of raping or indecently assaulting another girl and of having 256 indecent images of young girls on his computer.
Newsham, of Attwill Almshouses, Exeter, worked as a coach and bus driver for many years and his work included school runs and taking school parties all over the country, the court heard.
During a two-day trial, the court was told Newsham abused his position to offer the 11-year-old a trip to Disneyland Paris in 1998 and assaulted her at a hotel where they stayed.
Despite dismissing the charges as "ludicrous" and claiming his victim was lying, he was found guilty by a jury within an hour.
He had already admitted raping and abusing another girl in the 1990s, but claimed their relationship was a "long-running affair" when she was aged between nine and 14.
Remanding him in custody, Judge Phillip Wassall said: "You fall to be sentenced for these two indecent assaults and another series of sexual assaults including rape. You will receive a substantial custodial term for these matters."
He added that he was to make inquiries to see whether Newsham posed a substantial risk to children.
He said: "Those who assess the risk should be able to see what you said because I have never heard anything like it.  It amounted to enough in itself to find you are a dangerous offender."
A retired coach driver who abused a girl on a trip to Eurodisney in the late 1990s has been told he is a "dangerous offender".