Usage of antibiotics for fever depends on the condition and clinical findings in the baby though most of the fevers are viral... it's prudent to get your child examined by a pediatrician before starting any antibiotics.... of course safety I think u mean side effects  depends on the antibiotic used... your pediatrician will guide u In that...

Antibiotic should be prescribed by a doctor. If needed he will prescribe after diagnosis  of the condition. Antibiotics can be given to children but there has to be a valid reason like a bacterial infection.