DERRY, Pa. — A woman pushing a stroller across railroad tracks in western Pennsylvania was struck by a train and both she and her 2-year-old son were killed, police said.

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The 37-year-old Derry mother and three of her children were returning from a shopping trip early Friday evening, authorities said. They said she was struggling to push the stroller across the tracks when she and her toddler son were hit by a Norfolk Southern train at about 5 p.m. Her two young daughters managed to dart across the tracks and were not injured.

The victims' names have not been released pending notification of relatives.

A Norfolk Southern spokesman said the company is cooperating with the investigation but declined to comment further.

The crash happened less than 100 feet from where a 15-year-old was struck and killed by a train in July.