As Minneapolis public schools prepare to begin the first day of classes on Tuesday, police confirmed three more children were injured in last week’s shooting at the Annunciation Catholic School.

Minneapolis Police Department on Monday announced the revised number of injured, bringing the total amount of victims who were injured by gunfire to 21.

Authorities said 18 children between the ages of 6 and 15 were hurt in the shooting, along with three adults in their 80s who were attending mass at the time of the incident on Wednesday.

The gunfire erupted during morning Mass, when a 23-year-old shooter opened fire through the windows of the school’s church, police said.

Two children, 8-year-old Fletcher Merkel and 10-year-old Harper Moyski, died in the shooting, their families confirmed on Thursday.

“Yesterday, a coward decided to take our 8-year-old son, Fletcher, away from us. Because of their actions, we will never be allowed to hold him, talk to him, play with him, and watch him grow into the wonderful young man he was on the path to becoming,” Jesse Merkel, Fletcher’s father, said on Thursday.

Harper’s parents remembered her as a “bright, joyful and deeply loved 10-year-old whose laughter, kindness, and spirit touched everyone who knew her.”

Hennepin Healthcare said four patients — three children and one adult — remain hospitalized at the Hennepin County Medical Center.

While other Minneapolis schools are coming back into session with a substantially increased visible patrol presence, Annunciation will remain closed.

Police continue to actively investigate the shooter and have yet to determine a motive.

The shooter, who previously attended the school, died at the scene from a self-inflicted gunshot wound, authorities said last week.

“There has been conversation” with the shooter’s mother, Minneapolis Police Assistant Chief Christopher Gaiters said on Friday, though he did not elaborate.

Annique London, one mother of three daughters who all attended Annunciation in recent years, told ABC News she and her children feel a mix of community support and anxiety as school starts.

London’s daughter recently graduated from Annunciation — which teaches children in pre-K to eight grade — and will start high school nearby.

“She’s going to the public school Southwest High School and is terrified to go to school. And I don’t think she’s unique. I don’t even think the public school administration has yet come to terms with the support that might be needed for some students,” London said.

ABC News’ Ahmad Hemingway, Christiane Cordero and Briana Stewart contributed to this report.