Keira Knightley and Elisabeth Moss will headline a West End production of Lillian Hellman’s “The Children’s Hour.”Helmed by Ian Rickson (“The Seagull” and Broadway’s upcoming “Jerusalem”), the play is skedded to open in early 2011 although a theater has yet to be locked in. Sonia Friedman Prods. and Scott Landis are producing. Knightley appeared last season on the London stage in “The Misanthrope.” Moss starred on Broadway in the 2008 revival of “Speed-the-Plow.” Hellman’s 1934 drama about two teachers accused of having a lesbian affair has never been seen in the West End although Howard Davies helmed a production at the National Theater in 1994. The play has been filmed twice, once in 1936 by William Wyler as “These Three” and in 1961 as “The Loudest Whisper” with Audrey Hepburn and Shirley MacLaine.