Children often make errors in their grammatical constructions. This indicates they are learning:

The correct answer is morphology, which refers to the study of the structure and formation of words, including the rules for how words are formed and how their forms change to express different grammatical categories, such as tense, mood, voice, aspect, person, number, gender, and case. When children make errors in their grammatical constructions, it often stems from their developing understanding of how to manipulate morphemes, the smallest units of meaning in a language.

For example, a child might say "goed" instead of "went," demonstrating their grasp of the concept of past tense but challenging their ability to apply the correct morphological rule for irregular verbs. As children learn language, they go through stages where they apply rules broadly, even in situations where exceptions exist, exemplifying their developmental processes in morphology.

In contrast, pragmatics involves the use of language in social contexts and understanding the social rules of communication. Semantics is about the meaning of words and sentences rather than their grammatical structure. Phonology refers to the sounds of a language and how they interact, which is unrelated to grammatical errors in construction. Understanding grammar errors through the lens of morphology helps illustrate how children are actively engaging with and learning the complexities of their language.