The present study offers an original multi-level linguistic analysis of child speech in the 3-5 age group, combining a structured observational methodology with a qualitative-quantitative framework developed by the author. Unlike existing survey-based accounts, this paper proposes a three-tier Phonetic–Lexical–Grammatical (PLG) Developmental Profile as a practical diagnostic tool for assessing speech maturity in preschool children. The research was conducted on the basis of 120 spontaneous speech samples collected from 40 Kyrgyz-Russian bilingual children aged 3 to 5 years attending preschool institutions in Bishkek. The study identifies age-specific patterns of phonological simplification, lexical growth strategies, and syntactic complexity, and introduces a composite Speech Maturity Index (SMI) that integrates quantitative indicators across all three levels. The findings demonstrate that bilingual children in the studied cohort display a systematically accelerated grammatical development compared to monolingual norms while exhibiting specific phonological transfer patterns not previously described in the literature on Kyrgyz–Russian bilingualism at preschool age. The proposed PLG Profile and SMI are presented as replicable instruments suitable for use by preschool educators and speech therapists.