Updated 01/10/13 – 5:21 p.m.

CHICAGO (CBS) — Some parents of kids at a South Side elementary school were upset that they weren’t informed a 13-year-old boy had brought a gun and ammunition to the school on Wednesday, until they read about it the next day.

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CBS 2’s Derrick Blakley reports the parents were angry they didn’t learn about the incident from the school, but from reading about it on Facebook.

A 13-year-old boy was arrested at John L. Marsh Elementary School at 9822 S. Exchange Av. on Wednesday, after bringing an unloaded revolver and some bullets to school, and placing them in his locker.

Parents weren’t officially notified until students took home notes from the principal on Thursday. By then, some had already learned about it on Facebook, and said the notification from the school was too little, too late.

Grandmother Sylvia Campos said, “No notification, no nothing; word of mouth is how it got out.

She said that’s not good enough.

“Not when my baby’s here, no,” Campos said.

Students were on the playground around 1 p.m. Wednesday when officials heard that a boy was carrying bullets.

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The 13-year-old boy was arrested after authorities found a 3-inch knife in his pocket, and an unloaded gun and ammunition in his locker.

“This is ridiculous. He brought a gun to school. How did they know what kind of mental status this boy had? What if he came in ready to kill,” Olivia Castellano said.

Parents said there’s one security guard at the school, and one metal detector, but most students don’t enter through it.

Ald. John Pope (10th) said, “This school is generally very safe; good students, good parents, good facility.”

Pope tried to calm angry parents, but admitted he had no answers for the most troubling gun questions.

Jeanne Hernandez said she wanted to know, “Where did he get it from? How did he get it? How did he get the ammunition for it? I mean, where are the parents at for this child?”

The 13-year-old student was charged with unlawful use of a weapon. He appeared in Juvenile Court on Thursday. Prosecutors said he was ordered to adhere to a 6 p.m. curfew at least until his trial on Feb. 26.

Chicago Public Schools officials said the district will be re-examining security measures at Marsh, as well as better ways to notify parents there.

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The principal said he didn’t issue robocalls or text messages on Wednesday, because facts were still being gathered. All of those issues were expected to be discussed at the school in a meeting with parents on Friday.