Curiosity motivates exploration and is beneficial for learning, but curiosity is not always experienced when facing the unknown. Why do humans experience curiosity in some circumstances but not others? And how does this change across development? In this talk, I will present my recent work investigating whether explanation-seeking curiosity — curiosity about a "why" or "how" question — is selective in a way that is tuned to the epistemic aims of explanation. If curiosity is selective in this way, we would expect learners to be most curious when they are most likely to learn useful and generalizable explanations. Our results show that curiosity motivates explanation search selectively towards explanations that a learner believes hold promise for learning. However, in ongoing work, we find that the triggers of curiosity change between childhood and adulthood. Broadly, this research sheds light on how human learners across the lifespan decide when to seek information and what questions to ask.