(NewsNation) — Annunciation Catholic School in Minneapolis remained closed Thursday as officials continued to investigate a shooting that left two children dead and 17 people injured.

Police said a gunman approached the school's church around 8 a.m. local time and began shooting into the building, as children and adults gathered for Mass marking the start of the school day.

The children killed were 8 and 10 years old, according to officials. All the injured parishioners are expected to survive.

"These beautiful children at Annunciation, they should not have to go through this right now. They should be learning math and playing at recess and messing around in a cafeteria and playing with their friends. That's what childhood is about," said Minneapolis Mayor Jacob Frey.

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