Researchers have long debated the means by which children learn the argument structure of verbs. Making syntactic generalizations often entails learning the semantics of different verbs, complicating and delaying the acquisition process. This study investigates four- to twelve-year-olds' and adults' knowledge of animacy hierarchy restrictions on postverbal word order in Sesotho double object applicatives, constructions where verb semantics is kept constant. Performance on forced-choice elicited production tasks showed that four-year-olds have early knowledge of the animacy hierarchy restrictions, providing evidence of syntactic generalization even on low-frequency constructions. Although there were no verb frequency effects, performance was also better on the highest-frequency animacy constructions. The results suggest that learning restrictions on verb-argument structure is facilitated when verb semantics is not a confound, but that construction frequency also plays a role in mastering the argument structure of verbs.