Suggest Dosage Of Melatonin For Toddler

What would be the appropriate dose for a two year old toddler taking melatonin for sleep. The child does not suffer from any neurological dysfunctions at this time nor does he have a history. His mother wants to keep him asleep at night because he bothers her when he awakens his sister and they watch the showed that were DVR d program for them by Grandma. Is there a legal age limit before you should would start the medication on a toddler? Please and thank you.