The acquisition of the past tense has received substantial attention in the psycholinguistics literature, yet most studies report data from English or closely related Indo-European languages. We report on a past tense elicitation study on 136 4–6-year-old children that were acquiring a highly inflected Finno-Ugric (Uralic) language—Finnish. The children were tested on real and novel verbs (N = 120) exhibiting (1) productive, (2) semi-productive, or (3) non-productive inflectional processes manipulated for frequency and phonological neighbourhood density (PND). We found that Finnish children are sensitive to lemma/base frequency and PND when processing inflected words, suggesting that even though children were using suffixation processes, they were also paying attention to the item level properties of the past tense verbs. This paper contributes to the growing body of research suggesting a single analogical/associative mechanism is sufficient in processing both productive (i.e., regular-like) and non-productive (i.e., irregular-like) words. We argue that seemingly rule-like elements in inflectional morphology are an emergent property of the lexicon.