The present study examined the production of inalienable possession with body parts in Spanish among 20 school-age children of Mexican-born parents born and raised in the United States. The results were compared to those of 20 first-generation immigrant parents (main input providers), 27 Spanish-dominant children of similar age, and 12 Spanish monolingual parents living in Mexico. Group and individual results obtained via a question-and-answer task showed low proportion of clitic se plus the definite determiner (e.g. "Ella se rompió el brazo" 'She broke her arm') among the heritage children in their production of the inalienable construal. The heritage children significantly overextended the possessive determiner instead of the definite determiner in contrast to their parents, the Spanish-dominant children and monolingual parents. Results also showed a significant role for dominance and language experience in the degree of morphosyntactic variability among heritage children, supporting recent research. The higher the Spanish dominance and the more Spanish contact and use the heritage children had, the more they aligned closer to their parents and the Spanish-dominant children in the use of the definite determiner. There were no divergences with the use of the definite determiner in alienable contexts. We argue for protracted development in child heritage Spanish stemming from crosslinguistic influence effects, minority language dominance and linguistic experience.