Daily use of benadryl (diphenhydramine) for sleep aid on a 16 month old. are there long term side effects?

Likely ok: but the quality of sleep from Benadryl (diphenhydramine) has not been studied yet. Thus although it is safe, you may or may not be getting the sleep quality required for optimal health. If possible try to establish better sleep habit (avoid caffeine after noon, no bright light /TV in evening, no exercise in late evening, regular exercise etc).

CONTACT PEDIATRICIAN: I think that you should definitely contact your pediatrician about the sleep issues and the use of routine Benadryl (diphenhydramine) in a child.

Nothing major: Benadryl can alter the sleep pattern some with diminished time in deep (recuperative) sleep stage. I would never consider chronic use in an infant. I would encourage you to write down all your prior sleep related efforts along with what happens at bedtime.Bring this in to discuss with the kids doc.