This experimental study compares the acquisition of the English to- and for-dative alternation by L1 English, L1 Japanese, and L1 Korean children. It is well known that there are restrictions on the verbs that can enter into the dative alternation—for example, you can show the results to someone and show someone the results; and you can demonstrate the results to someone but you cannot *demonstrate someone the results. L1 children sometimes overextend the double-object variant to verbs that disallow it. One question we investigate is whether L2 children, like L1 children, overextend the double-object variant. A second question we probe is whether L2 children, like L2 adults, transfer properties of the L1 grammar. Japanese disallows all double-accusative constructions. Korean disallows them with analogues of to-dative verbs; but with analogues of for-dative verbs, Korean productively allows them—more broadly, in fact, than English—if the benefactive verbal morpheme cwu- is added. Results from an oral grammaticality judgment task show (a) that all groups allow illicit to-dative double-object forms and (b) that the Japanese—but not the Koreans—allow illicit for-dative double-object forms. This bifurcation, we argue, stems from the fact that Korean (but not Japanese) has an overt morphological licensor for double objects. We thus find evidence of both (a) overgeneralization, like in L1 acquisition, and (b) L1 influence, like in adult L2 acquisition, in this case from the (syntactic) argument-changing properties of overt morphology.