J.C.
My kids were exposed, so I asked the other kids' mom and our pediatrician how to recognize it. The pediatrician said, sudden onset, high fever, cough. Especially watch for the respiratory symptoms. Sometimes sore throat. The other mom agreed with the "sudden onset" part - we saw her daughter in the afternoon and she was happy and energetic, but by dinner time, she had a high fever and other symptoms.
You might want to check with your pediatrician about tamiflu or similar anti-viral, if the symptoms started within 48 hours. My neighbors' kids all recovered pretty easily with no complications, but it took each of them 5-7 days. I'm hearing the same story from other parents around here - it's unpleasant but not life-threatening for most people. Just keep in good contact with your pediatrician and I'm sure everything will be fine!