CAMBRIDGE — It was a very exciting and emotional afternoon Sept. 7 at Sandy Hill Elementary School, with real-life heroes, a birthday celebration and the surprise return of Senior Airman Keagan Rosario. And a little bit sneaky. Because Art Teacher Henry Rosario, who marked his 50th birthday on Wednesday, didn’t know his son would be there, or was even back in the country. Principal Marybeth Shellaberger and just a few of her staff – the better to keep the secret – arranged for Airman Rosario to surprise his father with the entire student body present, along with teachers, administrators, family and friends. Children, faculty and staff were called into the gym for a presentation on real-life heroes. When all were cross-legged on the floor, six teacher volunteers were blindfolded and seated up front. Including Mr. Rosario – see, it was all thought out very carefully. The teachers were asked to name a hero by his or her description. Harriet Tubman was one, a nurse was one, a firefighter and a police officer were others. Then, last of all, Mr. Rosario was asked to name a hero who was brave and dedicated — and out came his son, who has been away for 15 months, including a seven-month tour in Afghanistan. Mr. Rosario tore off his blindfold and the gym erupted in cheers, with the children waving small flags. There was hardly a dry eye in the house. The pair were joined by the rest of the family, Angelia Thompson-Rosario, and brothers Ian and Henry. Amid a crowd welcoming him home, Keagan said as he came out of the corner room into the gym, he had been, “Extremely excited. My heart was pounding.” With his eyes misty and red with emotion, Mr. Rosario said of their phone conversations during the long separation, “When I talked to him, I cried because I missed him so much.” “I always look forward to making my dad proud,” Keagan said. “I feel like he’s my hero, with the way he puts his life on the line for us,” Mr. Rosario said. “This is the ultimate birthday present.”