My 13 year son is suffering from astigmatism; wearing sunglasses with left 7.00 & right 6.5 so please suggest?

Correct eyeglasses. Astigmatism is a need for eyeglasses due to the eye being oval in shape. The correction is simply to grind a reverse oval into the eyeglasses. Astigmatism is not usually a big deal - it just sounds like a big deal. With the proper correction, vision can be excellent.
More info needed. If i read this correctly and he has 7 diopters of cylinder (astigmatism) in the right eye and 6.5 in the left, i would first rule out keratoconus by seeing an ophthalmologist, because those are high values. Rgps could be helpful as contact lenses and he could wear whatever sunglasses he wants over that. If he's just nearsighted at -7 and -6.5, then you could just try prescription glasses or cls.