In order for children to understand and reason about the world in an adult-like fashion, they need to learn that conceptual categories are organized in a hierarchical fashion (e.g., a dog is also an animal). While children learn from their first-hand observation of the world, social knowledge transmission via language can also play an important role in this learning. Previous studies have documented several cues in parental talk that can help children learn about conceptual hierarchy. However, these studies have used different datasets and methods that have made it difficult to compare the relative usefulness of various linguistic cues to conceptual knowledge and to test whether they scale up to naturalistic speech. Here, we study a large-scale corpus of English child-directed speech -- collected in North America and the UK -- and used a unified classification-based evaluation method which allowed us to investigate and compare cues that vary in terms of how explicit the information they offer is. We found the more explicit cues to be too sparse or too noisy in child-directed speech, making them unlikely to support robust learning. In contrast, the implicit cues offered a more reliable source of information. Further, we investigated developmental changes from 3 to 6 years of age, and we found no differences in the availability of these cues in the input. Our work confirms the utility of caregiver talk for conveying conceptual information and supporting the development of early taxonomic knowledge. It provides a first step toward a cognitive model that would combine perceptual- and language-based mechanisms, leading to a more comprehensive account of children's conceptual development.