Hello, Ideally speaking, 4 months old baby should consume breast milk only. If mother is able to produce enough breast milk to fulfill baby s hunger for round the clock, then by the end of 6 months age of baby breast milk should be the the only meal. After 6 months as baby grows, may need more food to fulfil his hunger, in that case formula feed may be started with guidance of Paediatrician. After 6 months we may start giving water to baby. After 6 months we may add fruit juices in baby s diet but still its 2nd choice of meal. 1st choice of diet is still Brest milk. Sometime mother may not be able to produce enough milk to fulfill baby s hunger in case of sever diseases like TB or HIV or simply emotional imbalance due to 1st pregnancy. In such cases baby should start on formula feed with guidance and supervision of Paediatrician for first 6 months and after 6 months fruit juices may be added gradually. So coming back to your doubt, Giving fruit juices to 4 months old baby is not recommended. Thanks & Take Care, Dr. Suraj D.