Hi Donna.
We (and Moo) found it a bit hard when he moved into his big bed too. Its all new to them and he will most probably be feeling very insecure about it all. Oliver too got very upset and it just broke my heart, so we just offered plenty of cuddles and reassurance.
We tried the putting him back in bed all the time too but he just didn't get the hint lol So after a few days we moved on to the gradual retreat method. Starting by sitting on his bed, avoiding eye contact and conversation..By day 2 we moved to the floor, then just moving closer to the door - little by little. Doing this seemed to ease his anxieties about the whole 'big bed' situ. Just as he was relaxed enough, but not quite asleep we'd leave the room, making no fuss or convo.
After a week or so of him being in his big bed we could see he was settled enough..he got to the stage where he'd go bounding into bed on his own. He did get out and potter about his room, but we used to just leave him to it..when he got tiered he got on his bed and went to kip.
It may take a little while, just stick with it..lots of cuddles and praise on a morning if he's done a whole night, good luck hun..HTH
