Mental growth
I would say that caregivers who read or sing to babies are encouraging and supporting babies' mental growth, because when you engage with them by reading to them, you are increasing their chance in learning new words or their memory process, because if it's a word they are familiar with because they hear it a lot, they are more likely to remember it and use it. Example: if you repeatedly address yourself as "mommy" in front of your child, your child will get the idea and address you as mommy. Same thing applies with singing, excpet I think this would be more effective because children love to sing along and engage in singing.
