This paper focuses on the acquisition of locative prepositional phrases in L1 Norwegian. We report on two production experiments with children acquiring Norwegian as their first language and compare the results to similar experiments conducted with Russian children. The results of the experiments show that Norwegian children at age 2 regularly produce locative utterances lacking overt prepositions, with the rate of preposition omission decreasing significantly by age 3. Furthermore, our results suggest that phonologically strong and semantically unambiguous locative items appear earlier in Norwegian children's utterances than their phonologically weak and semantically ambiguous counterparts. This conclusion is confirmed by a corpus study. We argue that our results are best captured by the Underspecified P Hypothesis (UPH; Mitrofanova, 2017), which assumes that, at early stages of grammatical development, the underlying structure of locative utterances is underspecified, with more complex functional representations emerging gradually based on the input. This approach predicts that the rate of acquisition in the domain of locative PPs should be influenced by the lexical properties of individual language-specific grammatical elements (such as frequency, morphological complexity, phonological salience, or semantic ambiguity). Our data from child Norwegian show that this prediction is borne out. Specifically, the results of our study suggest that phonologically more salient and semantically unambiguous items are mastered earlier than their ambiguous and phonologically less salient counterparts, despite the higher frequency of the latter in the input (Clahsen et al., 1996).