How did you get your babies to start napping in their cribs? My twins do great at night (I planned to do Ferber, but they never made it past 5 minutes before falling asleep). However, they've always napped in swings, bouncers, rock n plays, on me, etc. I tried to do graduated extinction for naps, after a mini bedtime routine, but my daughter was so upset. After a couple of 10 minute "CIO's," I gave up. Any advice?