Consistency is the key. We've just been doing this with our 2 year old - and still do some nights!

If we hear him get out of bed (or into the toys or cupboards) - we go charging in there and say 'Bed - NOW!' and if he doesn't run over and jump in himself, we pick him up and put him in...

Some nights you just have to do it many times But he's definately gotten better while we're consistent.

The other thing that's worked for us (strange as it may seem) - is also telling off his favourite toy The couple of times we've done this, he's stayed in bed!