We present in this article corpus analyses, two experiments, and a preliminary English-French comparison on children's acquisition of "wh"-in-situ. Our examination of 10,000 "wh"-questions from CHILDES reveals that the reported empirical picture of "wh"-question acquisition in English is incomplete: A type of "wh"-in-situ, probe questions (PQs), has been left out from most discussions despite its presence in child-directed speech. Unlike "wh"-in-situ echo questions (EQs), PQs are used to request new information, and parents frequently use PQs and fronted information-seeking questions in alternation. The fact that PQs share the pragmatic space with fronted "wh"-questions while involving fewer syntactic operations and exhibiting lower input frequency allows us to test both structure-based and frequency-based theories of syntax acquisition. Our comprehension task with 3;06-5;06-year-olds confirms that children accept and understand PQs as information seeking. On the other hand, results from a production task show a strong avoidance of "wh"-in-situ, which is in line with reported elicited data from French-speaking children. We reason that a structural economy-based approach alone is not sufficient to account for children's disfavor of "wh"-in-situ. Depending on the input frequency and consistency, as well as the number of variants licensed by the grammar of a given language, children may treat part of the input as uninformative and initially only learn from higher-frequent, more regularized input. Their intake is thus selective.