It is normal for the bottle to have air all the time. Because the air does not enter the bottle, the milk will not be sucked out. When your baby drinks milk, just make sure that the mouth is full and you will not usually drink the air into your stomach. It is best to pick up your child after each feeding and burp them to prevent them from burping and spitting up. If you choose a bottle for your child, it is best to choose a good quality one, and after each feeding, the bottle needs to be cleaned and disinfected in time to avoid bacterial growth, which can cause diarrhea in your baby. Usually pay attention to give your child more water to avoid your child getting fire. If formula feeding, the child is prone to constipation, it is best to eat some bananas properly.