As tiny beings, babies require quite a few things the average human would need, but in smaller portions or in different wavelengths. For instance, sunlight…it's not that the sun will kill a baby, but if exposed to more than a certain amount, it could be harmful to the child. So also music…depending on the genre and volume, what a regular person may consider soothing or relaxing may actually be more than a child can handle.
Lullabies are often sung by parents in calming children, putting them to sleep, or simply spending time with them. The simple lyrics, nature, and storyline of lullabies are usually intended for children, and are therefore suitable for them. A parent can rock a child to sleep with a lull-a-bye, calm a discontented child, or singalong with a playing child.