We don't remember exactly when it started or how long it's been going on (years? months?) but Simon has trouble falling asleep at night. I can remember when he was a baby and I could easily rock him to sleep at naptime, but usually gave up at nighttime and just put him in his crib awake. He rarely cried about it, so it wasn't a problem.
If I had to pick a time that it started becoming a problem, maybe it was when Simon finally stopped wearing night diapers. He would use "I'm going potty" as an excuse to leave his room multiple times before finally falling asleep.
But again, it wasn't really a problem because he didn't bother us and eventually fell asleep.
But then, one time we woke up to him screaming at 4am because he had fallen out of the bathtub. Why was he in the bathtub? He found a cockroach in there.
That was when we realized he must be getting up in the middle of the night too. But, he always put himself back to bed, so not a problem.
Then there was the time Alice woke up in the morning and found him asleep on her couch. Another time we found him asleep in the basement. Sometimes in the living room.
One time, he screamed in the middle of the night (because the cat scratched him) and when I got up, I discovered he had turned every light in the house on.
So we came up with a new plan. We put toys in his room so he would stay in there and play when he woke up. It sort of worked, except he would play far more than sleep. Sometimes he would play in his room and then fall asleep in the hallway.
The problem with Simon is that we don't have much leverage with him. He doesn't care about bribes. He doesn't care if we take away stuff. We bribed him with candy. He loves candy. We took away all the toys in his room. Nothing worked.
The current pattern (as of 11/25/17) is that we sit on the couch in his room until he falls asleep. This seems to keep him in his bed, and he soon falls asleep. Then he wakes up at 3 every morning crying for Zac. Zac goes in and resettles him. We don't know what time he wakes up in the morning, but we think it's pretty early.