J.G.
He may be old enough to fall for something like the "big boy bed fairy"... try talking to him about how important it is to sleep in his own bed all night since he is "big boy" now and make up some story about how this fairy comes to certain children and leaves a surprise when they stay in their bed all night. This worked for me when my daughter was getting out and coming in our room. The first night the fairy left her a little toy (I think it was a rubber frog?) then on and off we did this for a few weeks - stickers, etc. The other thing that helped us is to tell him sleeping in your bed is "all done" and that if he comes in you will walk him back to his room EVERY TIME. If he knows this will happen he wont keep coming back for long. I know its hard at 2 am, but consistently walk him back - tuck him in again - try not to linger. He will test you - he might get out 10 times the first night - just walk him back every time - the next night might be 5 times, and it should not last long. Good luck!