This paper investigates Spanish-speaking children's acquisition of ser and estar with adjectives. Studies based on production data have shown that ser and estar are acquired early. However, we know very little about how children acquire this knowledge based on the linguistic input they are exposed to. Production data of ser and estar by eleven children and their principal caretakers were collected in order to investigate whether and how children extract information from parental input. A qualitative analysis of both the children's natural production and their respective input indicated that children's choice of the copulas was related to the semantic and morphological properties of the adjectives they appear with, suggesting that children may use linguistic generalizations independent from the input in order to acquire ser and estar.