We never used pillows with our kids when they were in the crib. When we moved them to the toddler beds is when we gave them a pillow. That way it could easily slide off on the floor and not get hung up on crib bars. We gave them an adult size pillow and it never moved really. it was the entire width of the mattress on the toddler bed and just stayed in that 1 place.

Morgann has never had a pillow in her crib and won't get one until she moves into a big girl bed.