Until she is about 4 months old, your baby's tummy can hold only small amounts of milk at a time. Too much milk during feedings can cause your baby to spit up or be fussy. Spitting up can happen when your baby: Burps (called a wet burp).
The right amount of milk and/or food is the size of your baby's fist. Feed your baby this amount of milk and/or food about every 1 to 2 hours. By doing this, your baby will not barf. Do not OVER feed or give your baby to much milk unless you like to clean up your baby's barf. This also happens for adults too. If we eat or drink to much our bodies will also bring it up, as barf, as soon as it can.