According to the Texas Department of Public Safety, troopers conducted a traffic stop on Monday in the border city of Laredo. In a photo posted by investigators, the group is seen packed inside the back of the truck.
The driver of the truck is now being investigated by the Department of Homeland Security.
Last month, Gov. Greg Abbott deployed more than 1,000 DPS troopers and National Guard members to the border as part of Operation Lone Star - an initiative he first announced in March aimed at beefing up security at the border.
The governor later expanded those efforts to also tackle human trafficking at the border, including a plan for DPS troopers and Texas Rangers to interview unaccompanied minors that cross the border to identify potential human trafficking victims.
The Texas Tribune contributed to this report.