The initial phase of linguistic production by children is char- acterized by rote-learned, lexically restricted forms and con- structions. Only during later phases of language acquisition do they develop flexibility across a paradigm and mix lexical and grammatical material more freely. In the development of verb morphology, a correlation between the use of tense and aspect has been observed in many languages. It has been sug- gested that this leads to an intermediary state of paradigm cat- egorization based on temporal categories. So far the flexibility of individual verbs occurring in different tense-aspect combi- nations has not been examined in detail. Here we evaluate the flexibility of verb use in a large longitudinal corpus of 4 Rus- sian children. We compute the Shannon entropy of verb stems distributed over individual grammatical forms. Results show that children do not pass through a stage of paradigm cate- gorization based on aspecto-temporal categories. After a brief item-specific phase of rote learned forms, they quickly become flexible users of verbs in both aspects.