A couple of weeks ago we set up the second crib. Frog had been sleeping in a mini-pack-n-play in their room. Monkey Boy is a mover and we were afraid he would kick his sister or roll on top of her. Anyway, we needed the pack-n-play for Ms. K's naps. Since she can stand and is cruising, we needed a sleeping place where she was safe and couldn't climb out.
Anyway, we put the two cribs right up next to each other. I SWEAR I heard angels singing when we did this! Monkey boy can gaze at little Frog as they go to sleep.
Since then, Monkey Boy has slept through the night... wakes up smiling... and generally goes down for a nap with very little fuss!