I really want to buy my son some new clothes.
That sounds nice, why do you want to buy new clothes for him?
My son is a good boy and a straight A student.
It is good that you are buying him clothes. That is just part of being a parent.
I like to treat him to something nice every now and then.
I think it's really nice that you buy things for your son when he does well in school. It's very thoughtful of you.