Why do you want to change your style. If you look good in those clothes than stay with this style. I can suggest you one place named Clockwork-Orange (www.clockwork-orange.net) where you can get various designer t-shirts and jeans in reasonable rates.
The little boy the upper part of the body can wear a black series of short sleeve T-shirt. Let a person feel cool. Private parts can be equipped with a comfortable light blue jeans. With a pair of BanXie. If you can. In a top duck cap. You will be out of focus. !
It looks sharp when boys wear plaid collared shirts. That might be what you already where. If you do, then you can try black skinny jeans as well! But not a plaid shirt with black skinny jeans, that looks...not good.