Baghdad (CNN) -- Eleven-year-old Hajer Sami says she remembers her father. It's flashes of memory, really -- a smile, a laugh.
She was only 4 when he was killed, but she can't recall vivid memories of him and their family when it was whole.
Her family was torn apart when her father, a policeman, was gunned down seven years ago on the streets of Baghdad.
She struggles to comprehend why anyone would have wanted to kill her father or why some people detonate explosives in the middle of a crowd.
"Why do these people kill other people? Do they get paid money to do it?" she asks.
Why? It's a question likely asked by many at the Al Noor Children's Center in Baghdad's Sadr City, a Shiite enclave home to more than two million people.
Here, inside a rundown, two-story building, Hajer is one of the more than 300 children who have been orphaned -- most in the Islamic sense when a family loses its breadwinner. It's almost always the father.
Most have a place to stay, with a mother or a distant relative. The center serves as day care center with a twist, a place where the children can go for food, clothing and education.
In a city known for its violence, the center is full of children with tales of a parent lost to a bomb blast or a gunfight.
In some cases, it's a child whose parent was a suicide bomber.
"We don't differentiate," says Liqaa Al Aboudi, the center's director.
Nobody is sure just how many Iraqi children have lost a parent to the sectarian violence that gripped the country after the 2003 U.S.-led invasion. The Iraqi Orphanage Foundation puts the number in the millions, while the United Nations says it is hundreds of thousands.
Now with the death toll rising as Iraq battles extremist fighters who have taken over large swaths of the country and vowed to overthrow the government, more and more children are being brought to Al Noor.
Al Aboudi started the children's center in 2009 on the outskirts of Sadr City. Then there 10 children, she says.
"I feel like I am falling short of what I need to do for the children. I always hope they have more. I try to make them happy with clothes," says Al Aboudi.
"I feel bad for their mothers as salaries are really low and not enough to live on here in Iraq."
Hajer and her best friend, 11-year-old Baneen, sit on a brown couch at the center giggling.
They couldn't be more different. Hajer wears her hair pulled back in a green band with a pink bow, while Baneen covers her hair with a traditional Muslim headscarf known as a hijab.
Theirs is a friendship born from grief. Baneen, too, lost her father. He was killed when a bomb exploded 10 months ago in Sadr City, she says.
Baneen and her four siblings now live with her paternal grandparents, who don't have enough money to take care of all their needs.
Her 6-year-old brother, Ali, never strays far from his sister. During a conversation about what happened to their family, he hangs on her every word.
Asked want he wants at the children's center, he says better food. Hamburgers? Pizza? "Shawarma," he says.
Across the room, a woman bounces baby Zahra on her lap.
Zahra, 1, and her brother, 4-year-old Mustafa, were found playing among the bodies of their parents.
It was mid-afternoon on a cold January day when militants burst into the family's home on the northern outskirts of Baghdad, a neighborhood known as Husseiniya.
Was it a revenge killing? Was it sectarian?
"We don't know why it happened," says Um Sajjad, the children's aunt.
She doesn't like talking about what happened that day as she worries it will remind the children of what they have lost.