I babysit a little guy who slept with his parents until he was two. He had a really hard time learning to sleep on his own at naptime.
I did lay down with him to sleep for the first couple of months but soon grew really tired of it...So...here's what I did.
This Idea takes awhile...you have to be VERY patient
Instead of laying with him I placed a chair next to the bed and sat quietly reading when I put him to bed. He looked at me like I was crazy at first but I told him that it was time for nap and I was going to read while he slept.
It worked! He tried talking to me for a few minutes and then his eyes got droopy and he was out
The first day I tried to leave the room while he was sleeping and he woke up instantly...so back to my chair I went
In one day he was falling asleep ON HIS OWN with me sitting next to the bed.
Gradually,I began moving the chair further away until I reached the doorway. He was always a bit concerned with each transition but as long as he could see me he didn't cry.
The chair and I finally worked our way into the living room about week 4!
He would fall asleep looking at me and then I was free to do whatever I needed to do.
Week 5 I put him to bed, gave him a kiss and a "I love you" told him that I'd see him after nap and walked out of his view. He called for me , I told him that I was in the living room and would see him after nap and HE WENT RIGHT TO SLEEP!!!
It's been about a year now and he is doing GREAT! I had his parents do the same at their home and he no longer sleeps in their bed unless they ask him to.