Abstract
Children’s remarkable ability to acquire language remains one of the most fascinating questions in cognitive science. How do they develop sophisticated syntactic knowledge? To contribute to this question, the present study investigates the role of input and learning mechanisms by modeling child language acquisition across increasing age. Specifically, this study trains 30 baby language models (LMs) on naturalistic input directed to children up to ages 3 through 7 and compares their syntactic knowledge directly with that of children aged 3 to 7, focusing on the constraint on wanna contraction, a phenomenon not previously tested in language modeling. Furthermore, the study examines two major LM architectures: an autoregressive causal LM, represented by GPT, and a bidirectional masked LM, represented by RoBERTa. The results showed that children were sensitive to the constraint and displayed age-related development, but neither GPT-based nor RoBERTa-based baby models showed the same pattern. In this respect, the baby LMs do not seem to fully capture human-like development, possibly suggesting that the learning mechanisms underlying child language acquisition do not entirely align with the architectures tested here and cannot be reduced to input-driven learning alone within the context of these models.
- Anthology ID:
- 2026.babylm-main.5
- Volume:
- [Proceedings of the Second BabyLM Workshop](https://aclanthology.org/volumes/2026.babylm-main/)
- Month:
- October
- Year:
- 2026
- Address:
- Budapest, Hungary
- Editors:
- Leshem Choshen ,Ryan Cotterell ,Mustafa Omer Gul ,Jaap Jumelet ,Tal Linzen ,Aaron Mueller ,Suchir Salhan ,Raj Sanjay Shah ,Alex Warstadt ,Ethan Gotlieb Wilcox
- Venues:
- [BabyLM](https://aclanthology.org/venues/babylm/) |[WS](https://aclanthology.org/venues/ws/)
- SIG:
- Publisher:
- Association for Computational Linguistics
- Note:
- Pages:
- 50–64
- Language:
- URL:
- [https://aclanthology.org/2026.babylm-main.5/](https://aclanthology.org/2026.babylm-main.5/)
- DOI:
- Cite (ACL):
- Haerim Hwang. 2026. Can Child Language Acquisition be Modeled by Linear Causal or Bidirectional Masked Models Trained on Child-Directed Input?: A Comparison of Baby Language Models and Children in Acquiring Wanna Contraction . InProceedings of the Second BabyLM Workshop , pages 50–64, Budapest, Hungary. Association for Computational Linguistics.
- Cite (Informal):
- Can Child Language Acquisition be Modeled by Linear Causal or Bidirectional Masked Models Trained on Child-Directed Input?: A Comparison of Baby Language Models and Children in Acquiring Wanna Contraction (Hwang, BabyLM 2026)
- PDF:
- [https://aclanthology.org/2026.babylm-main.5.pdf](https://aclanthology.org/2026.babylm-main.5.pdf)