The flat rash is on the tops of his feet and is spreading up his legs. It's also on some parts of his arms. He has a few blisters in his mouth, his throat is a little sore. 
If you are not familiar with HFM, do not dispair, it's a simple disease.
Hand, foot and mouth disease (HFMD) is a common childhood illness that is caused by a viral infection (most commonly the Coxsackie A16 virus). It typically affects children under the age of 10 years, but older children and adults can also be affected.
"Symptoms generally start to appear 3-7 days after becoming infected with the virus, beginning with a mild fever, tiredness, reduced appetite, and sore throat. The characteristic features — mouth sores and skin rash — usually develop one or 2 days after the onset of fever.
The rash appears as flat or raised red spots, which may form blisters. The rash is not itchy, and usually affects the palms of the hands and soles of the feet."
http://www.mydr.com.au/kids-teens-health/hand-foot-and-mouth-disease
HFMD is usually a mild disease, and children generally recover within 7-10 days. There is no specific treatment for HFMD, and because the disease is caused by a virus, antibiotics are not effective. (Antibiotics can only be used to treat bacterial infections.) However, a simple pain reliever such as paracetamol is often all that is required to treat the symptoms.
So prayers that Sam will heal quickly and that it will not spread are much appreciated!
