C.W.
My son is 4.5 years and just recently started sleeping on his own! We tried crying it out-sleeping with him-having him sleep with us, etc. What has been working for us is a good bedtime routine and convincing that he is a big boy and has his bear friends to sleep with. Dad was actually the one to get it done. I worked nights for a bit and DAD did the routine and said good night-Did not shut the door however. I believe the fact that he can still hear us and what not helps him to stay in his room alone also not shutting the door.
I had a friend that when her son turned 6 he wasn't interested in sleeping with them any more.... The baby I am sure has a bit to do with it. Oh, my friend in AZ has a Dora blow up mattress next to her bed for when her daughter wakes up in the middle of the night-She can't go in bed with Mom and Dad-just next to them on her Dora bed. Also I have a friend that uses the T.V.- Not a idea for me but.... Good Luck!