Nancy Cartwright’s “Simpsons'” session as Bart with Placido Domingo, taped six months ago for airing next month, was not their first meeting. Nancy’s children and Placido’s grandchildren attend the same (private) school. And they also vacationed with them at Placido’s estate in Acapulco. As for the taping session when Placido was “Simpson-ized,” , Nancy says, “He was so funny and he kept presenting different ideas. He was having the best time–and to hear just one note of Placido set my heart flying.” (She had not heard him sing with L.A’s.Opera).