Hi ,
I work in this field so I will give you a quick run down.
His right eye is significantly stronger than the left and the / - power is a slight astigmatism power. With kids it is best to correct it at this stage because they can develop with the muscle imbalance and power a ineffective corrective ability where the eye cannot be corrected as it starts to shut down as its focus never recovers. Positive lenses are always thicker in the middle and as a pp has said the stock lenses especially in kids can be thick and heavy as they can be out of a large blank size (diametre), Pay alittle more for either grind / aspheric lenses...they will look alot better.
But in saying this usually with kids optoms or opthals can prescribe a certain prescription and it will be altered in 6 months after the kids have adjusted to the correction and often increase it. So in saying no it wont correct itself if you dont do nothing and may make the problem worse. But alot of kids do have this sort of prescription, let me know if I can help.