The children called Nate Henn "Oteka," or the strong one, and they "fell in love with Nate's wit, strength, character and steadfast friendship," San Diego-based Invisible Children, a group that helps child soldiers, said on its website.
Henn, 25, a former University of Delaware rugby player, had raised thousands of dollars in the United States for Ugandan children's education and had gone to the country to meet the students, according to Invisible Children.
Henn was on the rugby field in Kampala with some of the children when the bombs exploded Sunday, Invisible Children said. Henn's parents, who live in Raleigh, N.C., declined immediate comment. Early Monday, a truck delivered flowers to their two-story brick home in a quiet neighborhood among tall pine trees.
His sister Brynne Henn wrote on her Facebook page: "I just don't understand. Please pray."
Henn's former youth pastor, the Rev. Andrew Hudson, said Henn was a gentle, sincere young man with deep compassion for those in distress.
The pastor from Chelten Baptist Church in Dresher, Pa., said Henn knew that traveling in Africa could be dangerous. "Nate was willing to take that risk in order to provide hope and healing for precious children who were finding themselves in very difficult situations," Hudson said.
Henn was a psychology major at the University of Delaware from September 2003 to December 2008 but did not earn a degree, spokeswoman Meredith Chapman said. He graduated from Concord High School.
He played club rugby at the university in 2005-06 until an injury sidelined him, according to school officials and a teammate, Jason Vanterpool.
He was "always smiling, he was a really, really nice guy," Vanterpool said.
Former neighbor Melanie Mask recalled how Henn and other children would play football in the front yard of her home in the quiet, shady neighborhood in suburban Wilmington where he grew up. As a teenager in Wilmington, Henn volunteered at an orphanage and went on a church mission to Peru.
"He always wanted to help people; never met a stranger, ever," she said.
Mask described Henn as gregarious but sensitive, easily making friends in high school. She said girls vied to be his prom date and nicknamed him, "Nate the date."
Dozens of people were wounded in the attack, including at least three Americans from a Pennsylvania church group.
The brother of a man who was killed in terrorist bombings in Uganda was aboard an airplane that crashed at a North Carolina airport.
A family member who asked not to be identified said Kyle Henn was aboard the airplane that crashed around 3 p.m. Monday as it attempted a landing at Horace Williams Airport in Chapel Hill. One person died and two others were injured.
A UNC Health Care spokesman said Henn was in fair condition while the second survivor was in critical condition.
Nate Henn, a native of Wilmington, Del. whose parents live in Raleigh, was killed in Sunday's bombings. Many of the 74 people killed were watching the finals of the World Cup.
The plane was registered to Thomas F. Pitts LLC of Wilmington, Del.
Associated Press writers David Dishneau in Hagerstown, Md., Karen Mahabir in Washington and Mike Baker in Raleigh, N.C., contributed to this report.