I'm not a trained lawyer, but I did some quick research online regarding your question. According to the link below, it appears febrile seizures, in most instances, do not cause a child long-term health problems. Additionally, according to what's in the link, a full seizure workout, including an EEG and CT scan, is typically not required to be performed on kids who have suffered a febrile seizure. I've read that in medical malpractice cases, juries tend to judge a doctor's conduct on what other professionals would have done under similar circumstances.
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I am not an attorney. Your best plan of action at this point would be to speak with a medical malpractice attorney in your area. They would be able to look through your child's medical and treatment history and provide a clear answer regarding your potential legal options. They may even be able to explain the complicated medical malpractice laws specific to your state. Hope this helps.