How to sooth my son with HFMD? He can't take any solids anymore. Sometimes drinking water is also a problem.

Hugs. Your son has ulcer in his mouth/throat that makes eating/drinking painful. However, it's essential to ensure he stay hydrated during this period. You can ease his ulcer pains by offering him some chilled fruit smoothies or milk. Honey water will heal his ulcer too. Try to go easy on acidic fruits as it might sting his ulcer. Bananas milk shake will make him full & the sweet taste might encourage him to drink more