We present the results from four studies, two corpora and two experimental, which suggest that English- and German-speaking children (3;1-4;9 years) use multiple constraints to process and produce object relative clauses. Our two corpora studies show that children produce object relatives that reflect the distributional and discourse regularities of the input. Specifically, the results show that when children produce object relatives they most often do so with ( a) an inanimate head noun, and (b) a pronominal relative clause subject. Our experimental findings show that children use these constraints to process and produce this construction type. Moreover, when children were required to repeat the object relatives they most often use in naturalistic speech, the subject-object asymmetry in processing of relative clauses disappeared. We also report cross-linguistic differences in children's rate of acquisition which reflect properties of the input language. Overall, our results suggest that children are sensitive to the same constraints on relative clause processing as adults.