Please HELP me cant get my kids to sleep?

Okay so i have a 15 month old and my daughter will be two sunday. and well i cant get them to sleep in there bed tru the night. My daughter was sent to the nurologist (because she walks on her tiptoes) and well he asked about it and i told him he gave her melatonin ( probably spelled wrong) and it suppose to help her sleep well i give it to both they do go to sleep about 30-45 min after i give it to them then ina hr or two they wake up and go to my bed to sleep with my and my husband then they fall asleep and i take them back later they come back and this is the whole night till i give up and let them sleep with us cuz im so tiered and have taken them to there bed about 3 or 4 times. What can i do anyone had a problem like this please help me.