In French, when there is no lexical subject, the use of a subject personal pronoun is mandatory. When there is a lexical subject, the personal pronoun becomes optional. Children tend to produce a lot of these optional pronouns. The study uses two corpora of spontaneous language production in children aged 3 to 4 and in children aged 2 to 4 to demonstrate that this behaviour is typical of young children, as adults do not display it with the same frequency. This behaviour is shown to develop at the same time as the use of preverbal subject personal pronouns. So the children's behaviour could result from an automatic use of personal pronouns in other contexts. This would imply that children's constructions should not be considered as a copy of the adults', but as a specific construction pattern that appears during the course of language development.