My kid had the same problem when he was younger and problem was fixed when he was five by the way of Chinese medicine. We went to the western family doctor here, he said kids would grow out of it. It is true in a way, but some kids might not until adulthood if parents do not handle it the right way.
It could affect the brain development of the kids and had concentration problem, later a tough teenage years. Your kids might not have a good appetite either.
I started to learn Chinese medicine myself because of this and benefit so much from it.
What this comment said here was very right. You should follow this path and take this seriously if you want a very healthy kid.It is very hard for me to type Chinese, I can provide you more information if you need.