It is unlikely you have a viable lawsuit. Even if the hospital was negligent, or careless, in its diagnosis  (and note: being wrong does not by itself mean they were negligent; they must have been careless in some fashion--the law acknowledges that doctors, etc. are not infallible and do not always get it right, and only imposes liability when they do something wrong), there likely are insufficient damages to support meaningful monetary recovery. You can only, in a court of law, get compensation for the injury caused by the malpractice. If your child was sick or getting sick anyway, you could only recover compensation for the degree to which the two-day delay in diagnosis made things worse, such as any additional medical costs caused by the two-day delay. However, since medical malpractice suits are very expensvie to bring--you need your own medical expert--you would almost certainly spend far more on the lawsuit than you would recover, even if you won.