The children at Robb Elementary School in Uvalde, Texas, were two days away from their summer break when Tuesday's massacre unfolded.

They had visited the zoo and participated in a gifted-and-talented showcase, recent posts on the school's Facebook page showed. Tuesday was awards day, according to the calendar, and students were invited to wear a nice outfit and fun shoes as part of a "footloose and fancy" theme.

But at 11:43 a.m., a note was posted on the Facebook feed: "Please know at this time Robb Elementary is under a Lockdown Status due to gunshots in the area. The students and staff are safe in the building," it read.

Then came a second message: "There is an active shooter at Robb Elementary. Law enforcement is on site."

School administrators asked parents to stay away. The school serves about 570 children in second through fourth grades, nearly 90% of them Hispanic.

The details that came next were devastating: an 18-year-old gunman had opened fire at the school, killing 18 children and one adult, officials said.

Messages poured in from around the world, offering prayers and expressing outrage at yet another U.S. mass shooting.

"Our hearts are breaking for the families that have been affected by this evil," Susan Vanderwier of Indiana wrote on the school's Facebook page.

The school district said the elementary school, where the mission statement is "Live. Learn. Love. Lead," would remain closed for the final days of the school year.