Botox injections to the masseter muscle can reduce the volume of cheek musculature but if a patient has "chubby cheeks" due to fatty deposits in the buccal mucosa this is often treated with buccal fat removal directly. It may be best to discuss this in a 1-1 consultation with the surgeon to be sure what procedure is best suitable for you. Be sure to trust your face to a specialist and best of luck to you.
Botox treatment is used for treatment of enlarged masseter muscles but not "chubby cheeks". Without seeing a photo or evaluating you in person, it's hard to tell if you are a good candidate for this treatment.