The most common baby talk style is to create new words that are supposedly more comprehensible to the baby. Parents will point to a dog and refer to it as “bow-wow” or call a cat as “meaow”. You could say that they are both referring to the sound of the animal and hence justified. How do you explain referring to food as “num-num”? That is a close approximation of the sound that is made when a toothless infant attempts to eat, a parent had explained to me. Try it out. But does baby talk limit the amount of vocabulary the child picks up? Does that matter?