Matthew currently has chicken pox. For those of you who don't know what this is (and I assume that this is only a few) is a disease caused by a virus that causes little spots or blisters to appear all over your body, which then scab over and heal. Once you have had the disease you don't get again, accept in rare cases.
It only lasts a week, but he isn't allowed back to nursery for two weeks until the last of the scabs are coming off. Mandy and I have both had it as children so we won't catch it again. Although Mandy might go spare being stuck at home with a sick Matthew for two weeks.
I'm glad he has it now as it is the best time for him really. If you have this disease as an adult it is called shingles and is very painful apparently.
I'm quite sure he will be fine in a few days, although it does explain why he has been a bit naughty recently.