I'll be with my two kids, ages 11 and 13, who want to go up the Eiffel Tower. We plan to take the RER from Gare du Nord to Notre Dame for a quick look around (maybe climb the towers if the wait is not long), then ice cream at Berthillons or maybe lunch. Then hoof it to the Eiffel Tower. My question: how long of a walk from Notre Dame to the Eiffel Tower? And what's the best route -- right or left bank? Should we get pre-purchased tickets to go up the tower, or will the wait on a Wednesday in early November not be too bad? And finally, is there a direct route back to Gare du Nord from Eiffel Tower on the subway? Or would taking a cab be faster? (Have an 8 p.m. train to catch back to London.) Thanks much.