Help

First of all no more medicine. Your causing possible future health problems, and also getting there immune system use to the drug, therefore when they really need it it will not work. Every child is different, your child will go through phases and different sleep habits. My first suggestion is talk to your childs pediatrician.
I have 3 children each have had different sleeping habits. To really know how to answer your question, I would need to know what time are they waking up, when they are taking there daily nap, and how long is the nap?
My middle child had a similar problem, we gave her a night bear which we call Manty and when we give her manty she knows bed is coming soon. Now when we put to her bed Manty is waiting for her. If she had a day that was very exciting we will put a movie on for her to watch, CARS being her favorite so she has something to help her stay calm till she falls a sleep. Also make sure they have a full tummy which always helps them sleep better.