Yes, there is a natural treatment for thrush. Thrush is actually a yeast or candida Albicans of the mouth. It can occur at any age, and is often triggered by a change in the immune system especially following an antibiotic.
If you are breast feeding you can take a pro-biotic capsule, open it wet your finger dip it in the powder and apply it to the nipple before you nurse your baby. I encourage mom's to take the pro-biotic also, that way if you are the trigger you are treating both you and your baby.
If you are not breast feeding than I encourage you to get a pro-biotic for children and give it to your infant between feedings. It works best on an empty stomach and not as well if it is put into a bottle or food.