Background: At least two‐thirds of the world's children grow up in environments where more than one language is spoken. Despite the global predominance of multilingualism, much remains unknown regarding the language acquisition of children acquiring multiple languages compared with monolingual children. A greater understanding of multilingualism is crucial for speech–language pathologists given the increasing number of children being raised in linguistically diverse environments.

Aims: To investigate the expressive morphological abilities of multilingual children acquiring English, compared with monolingual children, at 3 years of age.

Methods & Procedures: Participants were 148 children (74 multilingual children; 74 matched monolingual children; mean age of 3 years 4 months) already participating in a larger prospective longitudinal cohort study of language development in Melbourne, Australia. Thirty‐one languages in addition to English were represented within the embedded cohort. All participants completed a direct language assessment to measure their expressive abilities across a range of English morphemes. The parents of the multilingual participants completed an interview regarding the children's language backgrounds and experiences.

Outcomes & Results: The Multilingual Group typically performed below the Monolingual Group in terms of their accurate use and mastery of English morphemes at 3 years of age, although variable expressive abilities were indicated within each group. The same morphemes were shown to be mastered by relatively higher proportions of each group. Likewise, the same forms were mastered by relatively lower proportions of each group. The results indicated similarities between the children's acquisition of English morphology, regardless of whether they were acquiring English only or in combination with another language(s) at 3 years of age.

Conclusions & Implications: This study found a range of similarities and differences between multilingual compared with monolingual children's acquisition of English morphology at 3 years of age. The findings have important implications for researchers and clinicians involved in the management of linguistically diverse populations by advancing knowledge of early multilingual English morpheme acquisition and building awareness of acquisition patterns among multilingual and monolingual English‐speaking children at 3 years of age.