The expression of negation is a privileged locus to study multimodal combinations (Morgenstern, 2014). There is a cross-modal continuity in the expression of negation speech acts, which are first mainly expressed by body actions, vocalizations, then by gestures and speech (Clark, 2004; Guidetti, 2005; Iverson, 2010; Zlatev & Andren, 2009). This study explores how body actions and gestures contribute to the expression of linguistic complexity in children aged 1 to 4. Using a multimodal approach, the analysis examines how children integrate gestures with their spoken and vocal productions to convey meanings and complex communicative intents. The data consists of longitudinal recordings of two monolingual children (one French and one English) in natural parent-child interactions filmed in their home environment. Findings reveal that co-speech gestures are not mere accompaniments to spoken utterances but play a crucial role in embodying complex linguistic structures. Three types of complexity were identified: (1) body actions and gestures that complement speech by adding semantic layers, (2) body actions and gestures that supplement speech by introducing additional predicates, and (3) body actions and gestures that serve as primary vehicles of meaning in instances where speech is syntactically simple. These results highlight that gestures and body actions can bridge the gap between cognitive intentions and linguistic output, revealing sophisticated cognitive processes that are not immediately visible through spoken analysis alone. The study argues for a re-evaluation of traditional definitions of language complexity, suggesting that multimodal elements are essential components of children’s communicative repertoire. By embodying complex meaning through synchronized gestures and body actions, children demonstrate advanced cognitive and linguistic abilities, offering new insights into the development of complex language structures in early childhood. Clark, E. V. (2003). First Language Acquisition. Cambridge University Press. Guidetti, M. (2005). Yes or no? How young French children combine gestures and speech to agree and refuse. Journal of Child Language, 32(04), 911–924. https://doi.org/10.1017/S0305000905007038 Iverson, J. M. (2010). Developing language in a developing body: The relationship between motor development and language development. Journal of Child Language, 37(02), 229–261. https://doi.org/10.1017/S0305000909990432 Morgenstern, Aliyah. (2014). Children’s multimodal language development. In Christiane F.cke (Ed.), Manual of language acquisition (pp. 123–142). Berlin & Boston: De Gruyter. https://doi.org/10.1515/9783110302257.123 Zlatev, J., & Andrén, M. (2009). Stages and transitions in children’s semiotic development. Studies in Language and Cognition, 308–401.