I've been an RN before retiring due to health problems. The condition sounds a lot like a candida infection (also known as thrush). Usually it will also cause white coating on the tongue which sometimes looks creamy or like cottage cheese residue. Any age person can get this condition. If the spots were small and splotchy streaks and mixed with red streaks it could be a strep infection. As for the thrush--Sometimes when a person takes too many antibiotics (if the child has been on any) they can kill off the good bacteria in the mouth as well as the bad, thus causing the thrush infection to grow. The more antibiotics you take for thrush, the worse it gets. Antifungal medication such as nystatin is usually a good medication to take. For children it comes in a liquidy solution that taste a lot like bananas. This medication is also called "swish and swallow". Thrush (candida) is very painful and can get under the roots of the teeth and into the gums causing extra severe pain. My advice would be to take the child to the doctor and let them rule out the white patches as being thrush versus strep. In the meantime, if the child is old enough to gargle, have him/her gargle warm salt water as this is closest to our natural body fluid and will help the healing process as well. Put about 1 tsp of non-iodized salt to 1 cup of lukewarm water. Great for mouth sores as well. But, if there is candida, you'll need an antifungal medication. Sometimes just stopping the medicatons will gradually make the conditon improve, but you don't want to wait that long and make the child suffer while the natural flora in the mouth is established. Cultured yogurt with pantothenic acid and products with acidolpholus are also good for restoring the natural flora within the mouth. Buttermilk also includes these to help the healing process if you can stomach drinking buttermilk or gargling with buttermilk. Hope this helps somewhat and your child feels better soon--but when in doubt, always consult a doctor. If the white streaks are from strep, the infection can develop into scarlentina (a mild form of scarlet fever that can cause a rash and if it becomes bad enough may cause heart damage) if you wait too long to find out what the patches are.
Only thing i can say is Oral Thrush, but usually it is painful. There are some drops you can get, maybe its worth trying them and see if it disappears?? I have been prescribed NILSTAT oral drops when i had this problem.