Sarah - I think an easy way to tell if they are dehydrated is to push into their pink skin and seehow long it takes for the blood to return. I think under 3secs is OK?
Its normally a day or two until they start getting really dehydrated, so the more you can get into now the better. Give him weak cordial - anything that he will drink is fine. Dont be stressed about a sweet tooth at the mo. Treats are the key. Jenna also like ice chips??
Good luck - I hope today is OK. can you call in sick?