I completely agree with Marina & Lynn O. My daughters, now 12 & 11, came into bed with us every night when they were little. Eventually, when they got too big (around 4) I too set up sleeping bags on my floor. They started out in their beds & if they got up, they were welcome to come sleep next to Mommy & Daddy's bed. They stopped that when they started Kindergarten. I never "forced" them to stop, they just did naturally. I never wanted my children to feel that they were not welcome in Mommy & Daddy's room, it's a security thing & when done right, creates a very content child. My son is 3 1/2 and still comes into bed every night at around 3am. I have never turned him away & I have already begun with the transition onto the floor next to us. I happen to feel that when your children want to be in the bed with Mommy & Daddy, it shows how much your children can "feel" the love between his/her parents, which is a beautiful thing. When your son is ready, he will begin to stay in his room through the night. Trust me, you'll miss it when it stops!
Hope this helps! Good luck ;)