This doctoral dissertation investigates various developmental parameters in the context of first language acquisition through a comparative triconstructional analysis (ditransitive, causative, and relative constructions) in children whose first language is English. The research is based on corpus analysis, during which the mentioned constructions were extracted and analysed from the English part of the CHILDES corpora. For a comprehensive interpretation and understanding of first language acquisition, intra-linguistic evidence (i.e., language phenomena related to syntax and lexicon) is observed and compared across three age-defined groups (0-3, 4-6, and 18+). Given the specificities of the three observed constructions, the analyses are tailored to their characteristics (such as frequency, complexity, and variability of certain lexemes and structural patterns appearing in these constructions). Simultaneously, they are conducted to allow not only inter-age group comparisons but also inter-constructional comparisons (such as the degree of similarity in the representation and frequency rankings of certain lexical units, as well as measures like structural and lexical complexity, including the mean length of utterance, lexical density, and type-token ratios). The main contribution of this research is the methodologically unique way of monitoring the parallel development of children's speech at the lexical, morphological, and syntactic levels, which analytically and interpretatively unifies the mentioned constructions through the lens of cognitive theories of language acquisition that are primarily based on the ‘usage-based’ model. Among other things, the research results show what can be described as a linguistic version of Pareto's principle, where all three age groups in the production of the observed constructions largely rely on a few lexical units in certain construction slots, and where the majority of their linguistic expression when it comes to said constructions is occupied by a relatively small number of structural patterns. Significant lexical and structural similarities among the same constructions were confirmed at several levels across the observed age groups, along with a more “conservative” language use and a more pronounced concentration of certain items and syntactic patterns with the declining of age. Furthermore, the ‘item-based’ claims about “simpler” constructions being more lexically restricted production-wise than more “complex” constructions was not confirmed; rather, an examination of certain lexical items used in specific construction slots showed that item-based tendencies are present in all constructions across all three age groups. In conclusion, the data on frequency and lexical and syntactic complexity obtained through comparative analysis of child and adult speech contribute to existing body of research on the nature of language acquisition and development.