This paper reports on a study of the acquisition of subject and object relative clauses by monolingual French speaking children aged 4-10 years, in Rimouski, Quebec. The children were tested for their comprehension of six types of relative sentences. A coordinate sentence control test was administered. An adult control group was also tested on the relative sentence test. The results are discussed within the framework of two principles proposed to account for language learning. Slobin's (1971) putative universal principle claims that the interruption and rearrangement of linguistic units is hard for both the child language learner and the adult. Sheldon (1974) has proposed the Parallel Function Hypothesis, which claims that sentences in which the identical NPs have the same grammatical function in their respective clauses are easier than sentences in which the identical NPs have different grammatical functions. The results of both the child and the adult study support the Parallel Function Hypothesis. The acquisition of French relative clauses follows the same order of acquisition that has been found for English relative clauses (Sheldon, 1974, Legum, 1975) and provides additional evidence for a parallel function constraint in language learning. An analysis of the errors that were made indicates other similarities and differences in the acquisition of French and English. (Author/CLK)