Omnicef and stomache

I have two children who were both prescribed Omnicef for bronchitis/sinus infections. My four year old began complaining within hours of severe stomache cramping and vomited followed the next morning by HUGE(golf ball and larger) hives all over her body(worse on her hands and feet) We stopped it immediately and swithched antibiotics. My 2 year old had already been on for a few days and had become very cranky, pacing back and forth, crying, mean,hitting,and repeating himself over and over. He was unable to sleep at night and developed what the doctor called excema mostly on his face and scalp. He completed the med yesteday and today broke out in full body hives (not as big as my daughters but very itchy and more severe around his eyes, hands and bottom. I was amazed that these side effect are supposedly not common but my two children who have both been on several different antibiotics for ear infections have never had any reaction. No more Omnicef at my house!!!!!