The suspect, who authorities have not named, is being held on unrelated charges in Schuylkill County, said state police in a release.
Investigators said the incident happened on the 7000 block of Lincoln Court in Lynn Township. A 9-year-old victim and three other children were walking their dog when the suspect pulled up in his truck, according to troopers.
Police said he opened the truck door and was not wearing pants.
Authorities previously circulated photos of the truck and a suspect description, and tips from residents helped track down the vehicle, said Trooper Nathan Branosky.
"The Pennsylvania State Police would like to thank the community for the countless tips and information received," he wrote in the release. "Further information will be provided at a later date and time."
Click here to follow Daily Voice Bethlehem and receive free news updates.