Four to six months: Onset to solid food. You should instance to wait until your baby is at least four months old before introducing her to anything other than breast milk or formula. You should start by offering your baby tiny amounts of baby cereal thinned with breast milk or formula. You can very likely introduce your baby to fruit juices that are thinned with water. You may want to agreeing off introducing orange juice for another month or two since orange juice may be too acidic.