Help 3 year old sleep

Julie • Full time mommy to 2 amazing little boys. A 3 year old and a baby born March 16th 2016 🍀
My 3 year old son takes forever to fall asleep. It doesn't matter how tired he is it will always take him about an hour to fall asleep sometimes longer. We have a consistent bedtime and routine, he is not getting too much sleep.. No screen time or sugary foods in the evenings... He goes to bed fine, lays still and quiet but just can't fall asleep. 
Any recommendations to help him drift off quickly? I don't mean melatonin or anything like that. Maybe essential oils? Anyone else dealt with this?