What happens if you have really bad eye sight at age 10 and need thick glasses for nearsightedness already?

Glasses/CLs. Some kids develop nearsightedness (myopia) early. In order to see better, they wear glasses and, when they are mature enough, can use contact lenses (cls). Kids are not appropriate candidates for any laser vision correction. Myopic people in general are slightly more at-risk for some eye diseases like glaucoma, so your child should be checked by an ophthalmologist at least yearly.
May Progress. Usually people who have high refractive errors (from near/far-sightedness or astig) at a young age may have a higher risk of progressive changes with age. This is seen most with nearsightedness and is called progressive myopia. How nearsighted a patient is needs to be determined by your doctor as many times patients feel that it is worse than statistics suggest. Contacts or surgery are options.