This paper examines the potential parallel between the ontogenetic and historical processes of grammaticalization of existential there. Taking Christopher Johnson's (Constructional grounding: The role of interpretational overlap in lexical and constructional acquisition, University of California, Berkeley, 1999, Constructional grounding: On the relation between deictic and existential there-constructions in acquisition, 2001, Developmental reinterpretation in first language acquisition, 2005) analysis of Child English as a starting point, the article tests the relevance of his theory of constructional grounding or developmental reinterpretation to the diachronic evolution of existential there-constructions in the earliest stages of the English language. The data show that, as in the case of child language acquisition, the existential pattern (There's a dog in the yard) is historically grounded in the deictic construction (There's the dog running around) and that double-locative overlap structures played a key role in the process of change.