Bedtime troubles

My 2 and 1/2 year old used to be a great sleeper.  You would put him to bed and he would go straight off to sleep, no fuss, and sleep through the night.  Back in March/April we transitioned him to a toddler bed, and still he was fine and used to go straight off to sleep.  However, a couple of weeks ago, maybe more, he starting coming out of his room after we had finished the bedtime routine and switched the lights out.
 
At first I would put him back to bed each time, however he would get more excited each time, and it would go on for over an hour.  I took a more hard lined approach, and when he started doing this I would hold his door closed so he couldn't get out, and he would then cry by the door.  Occasionally he would stop and go to sleep, but more often either me or DH would go in, put him in bed and sometimes he'd stop.
 
There's been some improvement, but not much.  But then this week I've had a revelation. He only does this when I'm in the house.  If I've gone out for the evening or just over bedtime, he goes straight off to sleep, or might come out once.  Last week, my mum was here and he started coming out and she told him I'd gone out (I was sitting in the kitchen at the time) and he went bad to bed and off to sleep.
 
So given that this behavouir is only for me, should I do something different?  Or should I keep holding his door closed, and eventually it'll get better?
 
My older twins were a nightmare at bedtime and we never really managed to get it that much better, partly because the pair of them were in the room playing together or getting up to mischief.  I can't let this go on for another couple of years....any advice gratefully received...

 

Can you let husband handle bedtime and 'be out' until your son gets back into a good bedtime habit?  If it works why not try it?

 

The thought has crossed my mind to do that, but i was worried that it might be worse when 'I'm back'.  But that said I don't really have anything to loose.
 
Tonight DH was out.  He was up, in and out of the room for over an hour.  And was still awake when DH came home, so he got him to go to sleep.  Talk about making me feel like the worlds worst mother...

 

It's not anything you are consciously doing and it won't last forever.

It's just a weird phase and until it's over, you get errands done and or meet up with a friend at night.

 

Some other things to try.....
 
What if you put bed rails on his bed so he can't get out of the bed?
 
Have you tried a sleep-wake clock?  You can get various kinds - ones with bunny awake and bunny in bed showing whether it's okay to get up or not,  Others are colors or such.
 
You could also try rewarding him for staying in bed.  For example, if he goes straight to bed, he gets a reward he likes - TV time, reading books with you, something like that that would motivate him to stay in bed.  Or a special stuffed animal that he only gets to keep when he stays in bed?
 
Another thought: my kids also pulled this for awhile, and mostly it was when they weren't tired, and when we made bedtime 15-20 minutes later so they were more tired, they went right to bed.

 

Have you asked him why he gets up, explained why it's important to stay in bed, and asked him what he needs to do that? Kids are great problem solvers.

 

Thanks for the suggestions.  I've had 2 nights where I've either been out or pretended to be out, so he's been going off to sleep.  I did spend some time tonight explaining why sleep was so important, but maybe I need to keep repeating it over and over.
 
We do have one of those nighttime daytime clocks in my older kids room, admittedly we don't use it now, so I could try it in his room and see if it makes a different.
 
Unfortunately he's a bit delayed on speaking so I can't really get him to put into words why he's getting up.  Hopefully the few things combined will help