My children have had the coxsackie virus a couple of times. Because this could be any of the below, I would seek professional advice from your pediatrician.
See the below information which was obtained from http://www.askdrsears.com/html/8/T082600.asp
TOP THREE CAUSES OF MOUTH SORES
Hand, foot and mouth disease (coxsackie virus) – this is by far the most common cause of mouth sores. It usually affects children ages 6 months to 3 years. Symptoms include:
High fever – often up to five days.
Severe fussiness – this is often the worst part of the illness.
Severe mouth pain or sore throat
Copious drooling
Refusal to eat or even drink
Rash – small, red or white spots may, but not always, appear on the hands or feet (thus the name of the illness). A red, lacy rash can also appear anywhere on the body.
Herpes virus– this is different from genital herpes. Symptoms are generally the same as for hand, foot, and mouth disease except that herpes does not cause spots or rash on the rest of the body. There are two unique points to know about herpes of the mouth:
Recurrence – once your child contracts this illness, the virus usually will dwell within the nerves inside the mouth for life. It can flare up during periods of stress, illness, or injury to the mouth. It can also cause cold sores on the lips throughout life.
Finger sores – occasionally the virus can spread to your child's fingertips from chewing on them during the illness. This will cause very large, white and red sores and swollen fingertips (different from the small sores and no finger swelling with hand, foot and mouth).
Canker sores– these are usually one or two large white and red sores in the mouth that result from trauma such as biting the tongue or bumping the lip.
HOW DO I TREAT MOUTH SORES?
Cold liquids – Popsicles, slushies or frozen juice can both sooth your child and provide needed fluids during this illness. Acidic foods like orange juice may be painful for your child
Medications
Acetaminophen or ibuprofen can help with the pain and fever. If needed, you can alternate between the two, giving something every three hours. Click on each for dosing.
Mylanta/benadryl/xylocaine mix – this is a very effective regimen that will sooth and numb the sores for a short period of time. The first two are over-the-counter, and the third is prescription. A pharmacist can mix them for you. This should only be used by children old enough to rinse and then SPIT it out. The xylocaine shouldn't be swallowed.
Benadryl– this antihistamine is available over- the-counter. It does nothing for the pain or fever, but it can help make your baby drowsy so he, and you, can get some rest. Click on it for dosing.
Acyclovir– this is a prescription anti-viral ointment that can be rubbed onto external sores. This only works for herpes sores that are on the outside lips or face. It works best if started at the first sign of a herpes or cold sore. Preferable when the itching begins and by past experience the child know the rash is soon to appear
IS MY CHILD CONTAGIOUS?
YES! It is VERY contagious, mostly via the saliva. When the fever has been gone for 2 days, and your child is back to her playful, happy self, then she is no longer contagious.
WHEN TO WORRY (AND NOT TO WORRY)
This can be a very painful and bothersome illness, but it is not dangerous. The expected course is fever, fussing, drooling, not eating, and barely drinking for up to five days. The sores and drooling can continue on longer than this, but they are usually less painful with time.
Dehydration– this is a big worry for parents during this illness since kids will go for days not seeming to drink much at all. Most children will get mildly dehydrated, but it is very rare for a child to get too dehydrated where medical intervention is necessary. Just do your best to push cold or frozen liquids, and your child should be okay. Click on dehydration for more info.
My child hasn't eaten for days! – Don't worry. Children can go without food for several days during an illness, as long as they are getting some fluids with sugar. Your child may lose weight during this time, but he'll gain it back when he's well!
CONSULT YOUR DOCTOR IF:
Your child has a fever more than five days.
Your child is acting unusually ill.
Your want your doctor to confirm the illness so you know what to expect.
Your child shows signs of moderate to severe dehydration. Click on it for more info.