It is quite common for babies to bring up 'curdled' milk, which is simply breast milk or formula that has begun the digestive process in the stomach. As long as your baby is active, gaining weight, and doesn't seem distressed after burping, it is often a normal part of development. However, if the vomiting increases significantly, occurs with force, or your baby seems to be in pain, consult your pediatrician to rule out issues like reflux or digestive sensitivity.