This paper investigates the use of -ing forms and bare verb forms in progressive contexts in cross-sectional data of L1-Russian L2-English children. It is proposed that child L2-learners are guided by the Uniqueness Principle (cf. Wexler & Culicover 1980; Pinker 1989; Clark 1987; among others), which leads them to restrict -ing forms to progressive contexts and bare verb forms to non-progressive contexts. The acquisition of progressive interpretation is furthermore shown to be independent of the acquisition of finiteness morphology. It is suggested that child L2-learners follow a developmental path similar to that of child L1-learners, but that, unlike L1-learners, they may also be influenced by L1-transfer.