This study is designed to analyze and chart the developmental patterns of children's plural acquisition, to find an appropriate account for the English plural development patterns found in children between two contrasting theoretical accounts: Symbolic-rule account and Connectionism, to find possible factors in children's own utterances and in caregiver input that influence children's plural acquisition, and to investigate whether the plural concept relates to the acquisition of number agreement of noun and determiner. For these purposes, the longitudinal records of conversation from two English-speaking children are examined. What is particularly being analyzed are the children's production of nouns with plural meaning, their caregivers' production of plural nouns, as well as the caregivers' feedback to the children's errors. The results of the analysis show that four development periods and a U-shaped curve are found in the plural development of the two children and that the Symbolic-rule account is more reliable for explaining the developmental changes in English plural acquisition. The results also convey that frequent production of a plural noun and its phonological constraint make up a degree of formal complexity which closely relates to children's plural learning. This suggests that the frequent use of a word with plural meaning helps master the form. The analysis of the caregivers' input demonstrates that using more diverse types of plural nouns in the caregivers' speech seems to help children master the plural inflection faster. It is also shown that any relevant feedback provided by the caregivers seems to stimulate the children's mastery of the plural inflection. Therefore, it is recommended that caregivers pay close attention to their children's speech and respond accordingly to their errors, thus prompting the children to master the language faster. Finally, the results of the analysis show that the two children master the agreement system of number-related determiners and the plural noun at different periods within the specified timeframe.