On Saturday, Jon Gosselin hit a playground in Wyomissing, Penn. with his 9-year-old twin daughters Mady and Cara and 6-year-old sextuplets Alexis, Hannah, Aaden, Collin, Leah and Joel. Joining the kids as they played on the swings and monkey bars: Ellen Ross, 23, his girlfriend of one month. "She is the first love interest to be introduced to his children," a source close to Jon, 33, tells Us of Ross, who lives in nearby Harrisburg, Penn. More on Jon & Kate Plus 8