A.H.
my son is five and still comes in to snuggle us in the night after using the potty or after bad dreams. Not sure if you have all the background on this child or what he has been through, but even children suffer trauma and stress and the subconscious works it out in the night, which may be what is happening. So this is why the child will want the reassurance that someone is there to keep him safe and secure.
I agree with the previous mom's post... this is a touchy situation and you have to build that bond - and it takes a while to build. I would just have patience as it sounds like this little one has been through quite a bit.
Even with my son now, I really don't mind if he comes in. We snuggle for a bit and I put him back in the bed. I feel the bigger deal I make of it - the worse the issue is. (as it can be for most cases.) However, if he is sick, he does understand now that he can get Mommy and Daddy sick if he comes into our bed at night. These are the nights he just wants one of us to snuggle in his bed for a few minutes for that reassurance. I see nothing wrong with it as it is the beginning foundation for them - it establishes trust, faith and security. When they are old enough to fully understand and comprehend the matter - then I will explain it more to my son that Mom and Dad really need a full-nights rest to feel our best as he just does not put the concept together yet...
Also - you may want to take the nap away or reduce it to thirty minutes. My son gave up naps at that age, to my dismay, but it helped him sleep better.