I would really like to know the answer to this because after eight kids I still haven't figured it out
. Currently our five year old is doing exactly the same as yours.
Here is what I know from the other kids over the years. They will continue to come to us at night until they have completed the following stages: teething, nightmares, night fears (dark, rain, thunder, teddy bears......), nursing, illnesses, wetting in the night, and waking up to use the toilet.
Some kids figured it out faster than others. Some would wet the bed and just roll over to a dry spot and continue sleeping. Some were heavy wetters and could go through two pullups and need to be changed.
So what we do is move them when they are good and asleep. Some are easier than others. We can usually buy a few hours of privacy this way and some extra room in the bed. The hard part is when you have more than one child then they can tag team and keep you up a lot of the night. That is my current problem. My six month old is teething and is waking up a lot in the night.
We find that usually by first grade they are not coming in to sleep with us anymore. Some kids will persist through age nine or beyond but that has been unusual in our family.
I don't find that rewards really work because sleeping with you is soooo rewarding all by itself and you can't really reason with a child in the middle of the night. When they wake up they are just focused on their immediate need and can not put it off for the promise of a sticker or treat later on.
A big part of the problem for us is that we are both tired. Sometimes just picking up a sleeping child and moving them takes more energy than I have. I can change them or take them to the potty but then trying to convince them into their own bed, do a back rub and all of that is not something I can really do in the middle of the night. I am just too tired. Dh has to go to work at four am anyways so he really is just too tired to be getting up with kids on the days he will have to leave for work. So I do all of the nighttime parenting on those nights and it is hard.