The study proceeds from the results of the previous studies showing that the distributional characteristics (frequency) of language input are crucial for the acquisition of prepositions (Savić & Anđelković, 2005, in preparation). The authors analyze deviations in the distribution of prepositions in children's spontaneous speech from the prediction made on the basis of the distributional characteristics of prepositions in adult language. The results show that, in comparison with adult language, only the prepositions "kod" (at, by, near, beside) and "sa" (with, from, off) deviate from the prediction. It was also found out that the unexpectedly early and frequent use of the preposition "kod" in child speech stemmed from the frequent use of this preposition in child-directed speech. On the other hand, the preposition "sa", which is very frequent in child-directed speech, is not present in children's production at the earliest age, because its homonymy makes it cognitively complex. The analysis of the reasons for such a deviation provided a basis for the discussion about the possible factors and mechanisms of development: the distributional characteristics of adult language are the major factor of acquisition, but the effects of conceptual and structural complexity were recorded as well.