This article investigates the acquisition of object shift in Norwegian child language. We show that object shift is complex derivationally, distributionally, and referentially, and propose a new analysis in terms of IP-internal topicalization. The results of an elicited production study with 27 monolingual Norwegian-speaking children (ages 4;05-7;00) reveal a prolonged delay in the acquisition of object shift with topical individuated pronominal objects. At the same time, we observe target-like placement and prosodic marking of contrastive, possessive, and indefinite pronouns, which do not shift. In our account of the observed delay we refer to the complexity models proposed by Yang (2002, 2004, 2005, 2010) and Hudson Kam & Newport (2005, 2009). In light of Yang's productivity model we argue that not shifting object pronouns is the rule, and OS is the exception. In light of Hudson Kam & Newport's approach to complexity, we argue that the children perceive OS as an inconsistent operation. (Contains 1 figure, 6 tables, and 16 footnotes.)