What do you have to lose? It's not going to hurt to take him to the eye doctor and if it turns out there's nothing wrong, then all you've wasted is a little time but you've gained valuable piece of mind. And if it turns out that there is a problem, early treatment might prevent it from progressing or even correct the problem. But make sure you find a doctor that specializes in children. At that age, you can't really fully on them telling you what they can or can't see during the exam but a doctor that is experienced in dealing with children will be able to better diagnose any problems.