Is there such a thing as eye-size surgery?

Best to seek in person consultation from an oculoplastic specialist to go over your concerns and goals. One eye can appear larger than the other either from one eye being more bulgy or the other eye being more droopy or other factors. The treatment depends on the exact problem.  For bulgy eye, orbital decompression can be helpful.

These deformities, such a Cruzon's, can make the eyes look relatively large.  Generally it is very important to distinguish between a normal variation and an actual craniofacial deformity.  That is because rebuilding the face is a major undertaking with a finite mortality rate.  We do not subject normal children to this sort of procedure for cosmetic reasons.  Does your child have an issue?  You did not post photographs so we can't answer that question.  Ask your pediatrician if your concerns are valid.  If so an assessment by the craniofacial surgery service at Stanford or to a more appropriate specialist, such as an oculoplastic surgeon, might be a reasonable place to start.

If you don't want to send photos, and I can understand your concern, there is no one here who can give you a diagnosis and some ideas on correction. See an eye surgeon. There are several reasons that you may be causing the asymmetry you are seeing and all can probably be corected. The most likely is ptosis.