Nouns to verbs and verbs to nouns: When do children acquire class extension rules for deverbal nouns and denominal verbs?

We investigated when children acquire class extension rules for denominal verbs and deverbal nouns using an intermodal preferential looking paradigm. We taught French-speaking 2.5-year-olds (mean age = 2 years, 8.56 months [2; 8.56], range = 2; 6-2; 11) and 3-year-olds (mean age = 3; 3.31, range = 3; 0-3; 5) novel parent nouns or verbs referring to unfamiliar instruments and their functions, and then tested their interpretation of both the parent word and its denominal verb or deverbal noun. Experiment 1 demonstrated that only the 3-year-olds understood the denominal verbs. Experiment 2 demonstrated that only 3-year-olds who learned the parent verbs were able to interpret the deverbal nouns correctly. These findings suggest that French-speaking children acquire class extension rules for denominal verbs and deverbal nouns by the age of 3 years and can demonstrate this knowledge as long as they are able to learn the parent words.