i will deny the arguments that babies do reason by using a psychological approach.
Now, in each of our brain, the frontal lobes are the parts of the brain that is responsible for higher psychological tasks such as reason. I will look at this in two ways. When a baby is born, the temporal lobes are not highly developed yet to unable the child to maintain reason.
Imagine the brain as an apartment block, the first block is the brain stem which is the most basic parts of the brain. This part is responsible for basic essential functions such as eating, breathing, sleeping and digestion and as time develops, the apartment blocks increase until you reach to the last level where reasoning is involved which takes place in the frontal lobes. These lobes are also responsible for movement and aspect of speech. Now, aspect of speech such as distinguishing various meaning significantly occurs childhood. A child would distinguished what is a ball. Now if one gives a child a spoon, the child will not say it is a ball because the brain now distinguished the word meaning of “ball” and this is part of reasoning. The child understands what is a ball and he will logically decide if a certain object is a ball.
For the case of babies, they do not reason. The acts of crying, feeling lonely comes from two ways. The first way is due to the activity of the brain stem which is responsible for survival instinct. The second is due to contact comfort where the child relies on the mother for warthm gained from face to face interaction where the child distinguished the mother’s face. This ensures that when the child feels danger, they rely to the mother. They do not reason out why they want to be with mother or purposely decide that they do not want to be the mother because even if the infant is noisy and rude, it will still go to the mother.