I have 4 year old twin boys. I have struggled greatly with bedtime-posting here, trying seemingly everything, going to a psychologist... There were a couple of things that finally worked. First, I gave in and sat with them instead of going back downstairs. Saved lots of energy. But, after several months, got tired of sitting there for 3-4 hours per night. Finally, I tried melatonin (after talking to the doctor) and it has made a world of difference. I discovered that they were overtired. As they got more tired at night, they get more wound up. I never would have though that boys who would stay up 3-4 hours after bedtime needed to go to bed earlier! But, if I let them stay up even an hour later, I pay.
Now, melatonin about 30 minutes before bed. And bedtime is an hour earlier than it was when they wouldn't sleep, and often they are asleep so I can go back downstairs within 15 minutes. The combination of melatonin, my change in expectations, and an earlier bedtime were what turned us around.