Child language acquisition is a fundamental topic in cognitive sciences as understanding language development can aid our understanding of cognition in general. The aim of this thesis is to explore inflectional noun morphology acquisition of Finnish-speaking children. There are two major methodologies applied to achieve the aim. A corpus consisting of 18 hours of child and child-direct speech was collected for a productivity analysis and for analyses of different input frequency effects on the child's accuracy with case marking and the likelihood of extending cases to incorrect contexts. Second, an experiment was designed to investigate how two-, four-, and six-year-old Finnish children comprehend transitive sentences. Study 1 (Chapter 2) investigated what linguistic productivity means. The study compared the mean number of inflections per noun between controlled samples of child speech at the ages of 1;7-1;8, and adult speech to compare the child's productivity with noun inflections against an adult speaker. The results showed a significant difference in productivity between the two samples, demonstrating the gradual emergence of linguistic productivity. Study 2 (Chapter 3) utilised the same naturalistic corpus as Study 1 to examine the impact of seven input frequency measures on the child's accuracy with noun case marking. The analysis demonstrates that while high type and token input frequencies did correlate with more accurate use of nouns compared to items with lower frequencies, high frequencies were also associated with increased likelihood of usage in incorrect contexts. Study 3 (Chapter 4) presents an experiment comparing children's comprehension of grammatical cues in transitive sentences. Case marking and word order were manipulated to establish how children of different ages utilise these cues in comprehension. The results demonstrated that all age groups performed most accurately when both cues supported each other whereas all age groups struggled with conflicting cues.