I have been a pediatric dental assistant for 8 years and have seen lots of cross bites. The dentist I work for now likes to see if the bite corrects it self when the permanent teeth erupt. The older dentist in our practice likes to do them as soon as the patient is compliant. It also matters what kind of cross bite your child has. Is it a posterior or an anterior? Most anterior cross bites are better being treated as soon as possible,but posterior ones can most of the time have different plans of treatment. It would be a good time to go to an orthodontist. They can give you lots of information and you don't have to jump right in and do active orthodontics if you don't want to. Talk to other moms who have children with braces on and you can go to the dentist most reccommended just to get yourself informed.Good luck!
Orthodontic treatment can be and is started at a much earlier age that it was done years ago. I believe that your son is not too young to get an examination with a orthodontist.