This paper examines aspects of variation in child language, and specifically how children express causal relations in complex sentences. Four particular types of variation were observed: (1) the order of clauses and the connectives used to link clauses; (2) mothers' causal statements; (3) interaction of language form and content, in the form of errors in causal statements; and (4) the interaction of language form and use, in terms of the effect of the speaking situation on the language forms chosen and the developmental sequence in the emergence of statements, questions, and responses. Eight children were seen in their homes periodically, from the time they were 24 to 41 months of age, and their speech while interacting with their parents and an investigator was recorded. The types of differences found among children in the expression of causal relations all had to do with aspects of the form and use of causal utterances, while the content of the children's causal utterances was remarkable similar. (CLK)