DD got one when she went into a bed at 16 months - just a junior pillow which is smaller and flatter than an adult one. You can get them at Kmart, Target etc - Tontine make them.

DS got a pillow just before his second birthday, he was still in the cot and a few days after he got it he started to sleep through the night...could be coincidence but after two years of sleep dramas with him I was pretty impressed.