This study investigated three- to five-year-olds’ ability to generalise knowledge of case inflection to novel nouns in Estonian, which has complex morphology and lacks a default declension pattern. We explored whether Estonian-speaking children use similar strategies to adults, and whether they default to a preferred pattern or use analogy to phonological neighbours.

We taught children novel nouns in nominative or allative case and elicited partitive and genitive case forms based on pictures of unfamiliar creatures. Participants included 66 children (3;0–6;0) and 21 adults. Because of multiple grammatical inflection patterns, children’s responses were compared with those of adults for variability, accuracy, and morphological neighbourhood density. Errors were analysed to reveal how children differed from adults.

Young children make use of varied available patterns, but find generalisation difficult. Children’s responses showed much variability, yet even three-year-olds used the same general declension patterns as adults. Accuracy increased with age but responses were not fully adult-like by age five. Neighbourhood density of responses increased with age, indicating that analogy over a larger store of examples underlies proficiency with productive noun inflection. Children did not default to the more transparent, affixal patterns available, preferring instead to use the more frequent, stem-changing patterns.