Screaming at 4 months of age is normal and is a milestone in language development. At 4 months of age, babbling and screaming, vocalizing to people and objects at 5 months of age, and turning the head when called by name at 6 months of age are all considered normal for language development. If your baby is unable to laugh at 3 months of age, unable to produce vowel sounds such as a and o at 2 months of age, and unable to cry loudly at 1 month of age, you should be aware of the possibility of speech delay and seek medical attention in a timely manner, taking into account whether your baby was born with a hearing impairment, so that you can give him/her early intervention and early treatment.