And one little boy brought them all a moment of levity.
"This little boy turns around, and composes himself, and he looks at me like he had just removed himself from the carnage and he says, 'Just saying, your house is very small,''' Rosen said. "I wanted to tell him, 'I love you. I love you.' ''
Rosen said Sandy Hook had always been a place of joy for him. He taught his 8-year-old grandson to ride his bike in the school parking lot and took his 4-year-old granddaughter to use the swings.
"I thought today how life has changed, how that ground has been marred, how that school has been desecrated,'' he said.
He said it wasn't his training as a psychologist that helped him that day -- it was being a grandparent.
A couple of hours after the last child left, a knock came on his door. It was a frantic mother who had heard that some children had taken refuge there. She was looking for her little boy.
"Her face looked frozen in terror,'' Rosen said, breaking down in tears.
"She thought maybe a miracle from God would have the child at my house,'' he said. Later, "I looked at the casualty list ... and his name was on it.''