Touch.

Gabbie always has to be touching someone to fall asleep at night.  If her leg is on mine, or we are holding hands, or even just her foot is touching my knee, she literally cannot fall asleep without it, it seems.  As a baby, I always rocked Gabbie to sleep, then placed her in her crib.  We did this every night until she was 20 months, when her sister was born.  Then she slept fine on her own for about a year, and has been in her current phase for about 9 months.  She's a very cuddly kid - she loves hugs and kisses.  Even when she is having a rough day and we are in the van, if I can hold her hand or rub her foot, it soothes her.  

Lilah is Miss Independent.  She will snuggle for about 3 seconds, then she's off and running again.  She likes to be read to, but prefers to fall asleep on her own.  We had to constantly hold her for several months, it seemed.  She was colicky and that meant lots of holding.  Then it was just over and she moved on. It's a precious moment if she sits down in my lap for a few minutes without me begging her to, and she only falls asleep on me if she's not feeling well.  She's a completely solitary sleeper.  

How interesting it is to see how they already differ, and to see how something so small could show us their true personalities.