A 5-year-old boy playing on train tracks fell and then froze up when he heard a locomotive approaching, leaving him unable to move before the train struck and killed him, police said.

Kevin Bradford and two other boys had sneaked past their grandmother to look for dinosaur bones on Thursday, police said.

Workers aboard the Union Pacific train traveling through this small North Texas town saw the boys on the tracks but couldn't stop in time despite braking, Union Pacific spokesman Joe Arbona said.

Kevin's 7-year-old brother and 5-year-old cousin made it safely off the tracks and ran home. Kevin's foot got caught in the tracks and he fell, officials said.

Watauga police chief Rande Benjamin said Kevin's death was an accident and charges would not be filed. A report was sent to Child Protective Services for review.

Texas ranks second in the U.S. for pedestrian-train fatalities. From January through July, 29 pedestrians died on Texas railroads, according to the Federal Railroad Administration.