A number of studies in language acquisition have dealt with parts of speech (PoS). Mainly, a growth of noun and verb diversity, as well as a variety of inflections have been evaluated separately from other PoSs. However, the PoSs play a unique functional role of building blocks interacted to each other in utterance, text, and discourse. The more a speech development progresses, the more skillfully and flexibly children manipulate with different PoSs to produce structurally well-organized and semantically transparent discourse. Our paper aims at analyzing a distribution of all PoSs in different discourse genres in preschool children. The cross-linguistic study was based on a corpus data of Russian (N = 12) and Lithuanian (N = 24) monolingual typically-developing 6-year-olds. Subcorpus No. 1 consisted of fictional narratives elicited according picture sequences. Following the RAIN methodology, Russian children were asked to tell a story according one picture sequence and then to retell a story according to another picture sequence; the sessions were separate by a few minutes of a conversation between a child and an experimenter. Lithuanian children were asked to tell a story according one picture sequence. To sum up, subcorpus No. 1 consistend of 24 narratives (2451 word tokens) (re-)told by Russian subjects and 24 narratives (2467 word tokens) told by Lithuanians. Subcorpus No.2 consisted of semi-structured dialogues between a child and an experimenter. Russian data (6710 word tokens) consisted of conversations based on standard comprehension questions about the (re-)told narratives; while Lithuanian data (5207 word tokens) consisted of semi-structured interwiev about a child’s favourite school subjects and activities. [...]