The buccal fat pads are located in the mid cheeks and lie between the inner and outer cheek muscles. As people age, this fat pad often gets smaller. If this is a hereditary issue and chubby cheeks run in your family, you might consider buccal fat reduction surgery. However, as you age, the cheeks also get thinner. So, for someone who is in their early to mid 20's I suggest waiting to see if this gets smaller as you age. If the buccal fat pads are reduced too early, my might be back 10 years later to restore fat to aging, thinning cheeks.
What many people refer to as chubby cheeks is often a zone of subcutaneous fat over an area below the bony cheeks known as the perioral mounds. This can be treated by small cannula liposuction from incisions inside the corners of the mouth.