A teacher at a private elementary school in New Jersey said as she celebrated her 100th birthday that being around children keeps her young. The Sundance School in North Plainfield held a party Friday for Agnes "Granny" Zhelesnik, believed to be the oldest active teacher in the United States, the (Newark) Star-Ledger reported. Zhelesnik started teaching cooking and sewing at the school when she was 81, when most of her contemporaries were retired or dead. "I suppose it's the children," Zhelesnik said when asked what has contributed to her long life. "It's a great life watching children grow up." Zhelesnik actually turns 100 Sunday. At Friday's party, the students sang "Happy Birthday," Benjamin Fox, the school's principal, read letters from President Obama and Gov. Chris Christie and North Plainfield Mayor Michael Giordano read a proclamation in the teacher's honor. Zhelesnik told the Star-Ledger she would rather have spent the day doing her job but was "going to live with" the party. Her daughter, Agnes Arakelian, who also teaches at Sundance, a granddaughter and great-granddaughter were at the party. At 10, Ashwin Sanjay, a student at the school, is one-tenth Zhelesnik's age. "She's so lively, you don't think that she's one hundred years old," Ashwin told the newspaper. "Her aura is so young."