My daughter was great at settling down for bedtime when she was about six months old. Because of our teen son's athletic schedule we threw her off schedule around 9 months and she was a bear to settle down every since. She is now almost 4 and we believe we have finally tamed the bear. It is not perfect but MUCH better than before. Here is what we did:
Her new daycare is more challenging than her old one (loved the old one but there was no curriculm and I believe she was BORED!) so we think she is more mentally tired when she comes home. We insure that she has her bath before that very fine window of opportunity (you know, when she is tired and may lay down but before she is over tired and can't settle down). For us, that time is bath by 8 pm so she will be asleep by 8:30 pm. If we miss this, she is still wired when we go to bed.
She has always been a night owl but will then sleep through the night. If we don't have her asleep by 9 pm she is a bear in the am. I know it sounds late but if she goes down any earlier, she is awake WAY too early.
Another thing we did just before the daycare switch was we removed all the toxic chemicals in our home...we swithched to non-toxic cleaning products, shampoos, toothpaste, laundry detergent...everything.
I don't personally agree with giving kids something to sleep (unless there is a medical reason) because then they become dependant on it. I do know that friends of my sister have given their kids Melatonin. My sister's doctor said it was safe and she did research it...supposed to be a vitamin that is safe. I don't have any first hand knowledge but was told to be sure they have at least 8 hours to sleep if you give it (sister said more like 10 hours). I would think if you were going to give something a vitamin would be better than regular medication but either way use caution.