WASHINGTON - U.S. Rep. Barney Frank [related, bio] will film an ad defending same-sex parenting in response to the flap over a PBS children's program denounced by the Bush administration for showing kids with lesbian mothers. The gay-rights group Family Pride Coalition asked the Newton Democrat to appear in the public service announcement after Bush Secretary of Education Margaret Spellings warned PBS in January not to show an episode of ``Postcards from Buster.'' PBS decided not to distribute the episode in which an animated rabbit visits Vermont to learn about making maple syrup with real children, two of whose parents...