In a syntactic priming paradigm, three- and four-year-old children and adults described transitive events after hearing thematically and lexically unrelated active and short passive prime descriptions. Both groups were more likely to produce full passive descriptions (the king is being scratched by the tiger) following short passive primes (the girls are being shocked) than active primes (the sheep is shocking the girl). These results suggest that by four, children have (shared) abstract syntactic representations for both short and full passives, contrary to previous proposals (e.g., Horgan, 1978).
Messenger, K., Branigan, H. P., & McLean, J. F. (2011). Evidence for (shared) abstract structure underlying children’s short and full passives. Cognition, 121(2), 268-274. https://doi.org/10.1016/j.cognition.2011.07.003