This research was conducted to determine the utterances that can be produced by a child and the simplification process that occurs in the utterances produced. The subject of this study is female twins aged 1 year 9 months. This study uses the method of observation, the researcher observes the two children, records and takes note the words spoken. The researcher participates in communicating with these children. Furthermore, the data that has been obtained in the form of records is transcribed into written form. The list of writings that have been obtained is then identified to find out the simplification process that occurs by comparing with the utterances that should be according to the dictionary and simplification theory in language acquisition. Data that has been analysed are then presented in tabular form and also presented with sentences. The results showed that there were several simplification processes for the utterances produced in the form of substance, reduction and word structure simplification. These two children are able to produce /m/, /k/. /t/, /d/, /p/, /n/, /b/, /a/, /o/,/i/, /ɑː/, /e/.

A comparative analysis is needed between the two languages or known as contrastive analysis to identify their structural similarities and differences so that the material and methods of teaching will be appropriate. Further than that, this paper is aimed to give a clear understanding about how Indonesian differs from English in the sense of its language features, especially in plural form. It is known that the structure of the plural between English and Indonesian is different although some similarities were found. Indonesian learners will find it difficult to learn plural words because in terms of word formation, English and Indonesian are very different. The formation of plural words in English is through the process of affixation, while in Indonesian, the formation of plural is through reduplication and addition of quantifier and number. It is necessary to give more explanations and exercises to learn the plural of English because with a lot of practice, it is hoped that Indonesian learners will start to get used to the formation of the plurals.