The grammatical subject is a multi-faceted linguistic notion embedded in morphology, syntax and discourse-pragmatics. In Hebrew, grammatical subjects are associated with two distinct word orders, differing along grammatical, semantic, and pragmatic axes. The study examines the growth and proliferation of Hebrew grammatical subjects in the spontaneous speech of preschool children in a Usage-Based perspective, taking into account inflectional, syntactic and semantic properties of the clause side by side with discursive information. The corpus used for this study consisted of the recordings of 54 children in six age groups from two to eight years, engaged in triadic peer talk. Subject, predicate morphology and word order were coded, and utterances were coded according to their conversational roles. Using cluster analysis, each age group was found to have a characteristic usage pattern of subjects with associated syntactic, semantic and discursive properties, underscoring the acquisition and development of grammatical subjects in Hebrew. The usage patterns emerging from the current corpus are taken as a manifestation of the Discourse Profile Constructions notion: probabilistic form-function correlations consisting of multiple sources of formal and functional information, pairing a usage pattern of clauses with a unified construal and discourse function. Three Discourse Profile Constructions emerged from the data: joint action planning, conversational narrative, and conversational presentation. Each of these was associated with a different patterning of lexical or pronominal subjects coupled with predicates with specific temporal features and different word order. These findings suggest that gaining command of the subject category is linked to communicative functions in development.