This study investigates the language profiles of Mandarin-speaking children with Developmental Language Disorder (DLD) and those with Autistic Language Impairment (ALI) through their repetition of passive sentences. It examines both long and short passives, predicting worse performance for the former structures than the latter. 15 children with DLD (aged 4;0–6;3), 18 children with ALI (aged 4;7–6;0), and 22 typically developing age-matched (TDA) children (aged 4;4–5;11) repeated 10 long and 10 short passives, the latter including manner adverbs to match the long passives’ length. Unexpectedly, no clear advantage for short over long passives emerged across groups. Both children with DLD and those with ALI performed less well than their TDA peers, with children with ALI slightly outperforming those with DLD. Both groups employed non-target and simpler responses to mitigate syntactic complexity, with notable differences in strategy between children with DLD and those with ALI. The study reveals syntactic difficulties in children with DLD and ALI, with more pronounced impairment in DLD. The Edge Feature Underspecification Hypothesis may account for these challenges, suggesting that the underspecified EF [+Topic] leads to alternative strategies. Additionally, the difficulty with manner adverbs might contribute to challenges with short passives, and children with ALI showed more pragmatic errors.