This study investigates how derivational complexity interacts with first language (L1) properties, second language (L2) input, age of first exposure to the target language, and length of exposure in child L2 acquisition. We compared elicited production of "wh"-questions in French in two groups of 15 participants each, one with L1 English (mean age 8 years 10 months or 8;10) and one with L1 Dutch (mean age 6;3), which were further subdivided into subgroups matched for the different variables under examination. Although in their L1s "wh"-questions display "wh"-movement and subject-verb/aux inversion, the learners did not perform similarly. A high number of "wh"-in-situ questions (i.e. the least complex option) was produced by the L1-English children, suggesting that derivational complexity can override L1 influence. In the L1-Dutch group, questions with overt "wh"-movement were more frequent. This may stem from the influence of generalized XP-movement to the left periphery in Dutch. Inversion (i.e. the most complex option) was rare in both groups and was related to contact with formal schooling. These results hold across the different subgroups, which suggests not only that complexity plays a role in child L2 acquisition, but also that its effects may differ according to the properties of the L1.