My, at the time, 7 year old son had it. He was in the hospital for 6 days. Scariest thing we had to go through as parents. Made me very great full for an otherwise healthy child. At 18 months I would think shed be ok as the symptoms seem to subside faster the younger they are. As someone else stated, I'd be worried that your 10 year old would get it. The older they are the worse the symptoms. Good luck and I hope everyone gets back to 100% quickly. Sick kids are no fun.