My kids were 6,4, and 3. They were also being naughty and not staying in bed when it was lights out.
The excuses grew every night, and the sneaking out to the top of the stairs grew incessant. But neither my husband nor I wanted to discipline too harshly because whenever we "laid down the law" it would delay bedtime even longer for a tantrum.
I don't like bed time tantrums.
Enter in Miss Spider's Bedtime Story App (affiliate link).
My son was obsessed with it for whatever reason. Essentially the little bugs are not going to bed when they're supposed to, so the parents make a reward chart called a wishing web. When they reach the top of the chart, they go to a carnival.
It's a really cute app, and as soon as I told my kids we were going to make a wishing web, they knew what I meant and were super excited.
We put the reward chart up and if they stayed in bed we'd move them up one, if the got out of bed they'd wake up in the morning and see that they were still at the same spot.
It helped that we didn't make a big deal out of them not moving up, other than a warning, until morning so there weren't any tantrums, right when we wanted them in bed. Another thing was we never threatened to move them down.
All it took was my girls reaching the top and getting prizes before my son one time before they were completely different children when it came to staying in bed. We kept using it until they developed the habit of staying in bed.
I highly recommend checking out the app if you have a Kindle or another compatible device, and making a reward chart for bedtime, it certainly worked for us.