Whilst certain verbs may appear in both the intransitive inchoative and the transitive causative constructions (The ball rolled/The man rolled the ball), others may appear in only the former (The man laughed/*The joke laughed the man). Some accounts argue that children acquire these restrictions using only (or mainly) statistical learning mechanisms such as entrenchment and pre-emption. Others have argued that verb semantics are also important. To test these competing accounts, adults (Experiment 1) and children aged 5–6 and 9–10 (Experiment 2) were taught novel verbs designed to be construed — on the basis of their semantics — as either intransitive-only or alternating. In support of the latter claim, participants' grammaticality judgments revealed that even the youngest group respected these semantic constraints. Frequency (entrenchment) effects were observed for familiar, but not novel, verbs (Experiment 1). We interpret these findings in the light of a new theoretical account designed to yield effects of both verb semantics and entrenchment/pre-emption.