To begin, we review three theoretical problem areas in the field of research into phonological variation in children. Next, we present the results of a cross-sectional study of two groups of children, aged 6 to 7 years and 10 to 12 years, relating to the deletion of post-consonantal word-final /R/ in French (production and judgments of acceptability). In an experimental study, we then examine the mechanism involved in the learning of words with a variable /R/. Finally, the interpretation of the results within the framework of a cognitive conception of variation leads us to four conclusions: (i) children have a tendency to copy adult surface forms rather than to encode a variable rule; (ii) orthography causes the late encoding of certain variable /R/s; (iii) the establishment of linguistic factors precedes that of social factors; and (iv) age-related changes are not guided by the sociolinguistic value that groups consciously attribute to the variables.