4 year old sleep problems

Hi, does anyone have any advice for me...my 4 year old will not for the life of him stay in his own bed all night long. He falls asleep in his bed every night by himself, and sleeps in there till about 1-3am depending when he wakes up. Then once he does wake, he comes straight to our bed. We are really wanting another baby and I'm afraid if I don't break this habit he will wake the baby when it does come around to the time! Any advice will help!!

-desperate momma who wants her bed back...