Contraction of want to to wanna is sometimes possible (e.g., Who do you want to/wanna stay with ___ ?), but sometimes impossible (e.g., Who do you want ___ to/*wanna stay?). This contrast is attributable to the grammatical constraint that a wh-trace blocks the contraction of want and to. Most first language (L1) and second language (L2) acquisition studies testing learner knowledge of this constraint have used elicited production tasks and focused on adult participants, with inconsistent results. Using a child-friendly acceptability judgment task, the current study shows that children as young as 3;11 and both child and adult L2 learners have target-like knowledge of the constraint on wanna contraction. This result is in line with the position that L1 acquisition, child L2 acquisition, and adult L2 acquisition are qualitatively similar.