The cross-categorical use of nouns and verbs poses a challenging problem to young language learners because they are known to be less willing to accept that a single form of a word be used for more than one linguistic purpose (e.g., one-form/one-function principle). The present study investigated whether children under 3 years of age are able to quickly understand the cross-categorical use of object-function denoting nouns (e.g., "This is a nice brush") as denominal verbs (e.g., "Brush your teeth") when the semantic relationship between the objects, referred to by the nouns, and their functions, referred to by the denominal verbs, is transparent. French-speaking 2.5-year-olds were taught the cross-categorical use of three novel parent noun and denominal verb pairs by presenting these pairs with semantic information coupled with noun and verb distributional cues. The results from Experiment 1 showed that, contrary to the one-form/one-function principle, 2.5-year-old children were able to fast-map the novel object-function noun-verb pairs onto novel objects and actions they had never seen before after three exemplars were shown. However, the results from Experiment 2 indicated that after being taught the cross-categorical use of two novel object-function noun-verb pairs, 2.5-year-olds were not able to interpret the third novel object-function noun-verb pair correctly when it was presented with semantic information coupled with noun distributional cues only. These findings suggest that although 2.5-year-olds do not have a strong one-form/one-function mapping constraint, they are not able to quickly form abstract class extension rules that enable them to immediately understand the cross-categorical use of new noun-verb pairs they have not heard before.