Nouns are among the easiest words for children to learn because they:

Nouns are among the easiest words for children to learn because they prefer more to map new names to objects rather than to actions or functions that the objects do and have.  Nouns can stand alone, unlike verbs that need performance to label the actions. Once they know the names of the objects or the noun, they will eventually learn the actions or verb. 

Ithink it would be choices a and b. hope this !