McCandless and Robinson were on a dirt road just north of Camperville in Coalville when the accident occurred.
There was alcohol at the scene, but investigators do not know if it was a contributing factor to the accident.
"While we don't know yet if it was a contributing factor, alcohol and off-highway vehicles do not mix," Stucki said.
McCandless and Robinson were not wearing helmets, which are not required when operating the side-by-sides, but are required for ATVs and motorbikes for everybody under 18.
"But even adults, if people put on those helmets, you don't know what lives could be saved," Stucki said.
The cause for the accident is unknown and is under investigation.