Cross-lagged panel analysis was used to examine associations between two joint engagement variables; higher order supported joint engagement and higher order supported joint engagement that co-occurs with caregiver's follow-in talk (higher order supported joint engagement + follow-in), and expressive and receptive vocabulary in a group of young autistic children (n = 91) with language delay (mean chronological age = 39 months). Variables were measured twice, 8 months apart. Coefficients for cross-lagged variable pairs were derived from structural equation models. Early higher order supported joint engagement was significantly associated with later expressive and receptive vocabulary (bs = 0.18 and 0.26, respectively), and early higher order supported joint engagement + follow-in was significantly associated with later expressive and receptive vocabulary (bs = 0.14 and 0.15, respectively). Associations between early vocabulary and later joint engagement were not significant. Linear contrasts between cross-lagged associations did not show a significantly superior association for any early joint engagement variables and later vocabulary variables. However, our results suggest that higher order supported joint engagement and higher order supported joint engagement + follow-in may be useful initial intervention targets for developmental interventions aimed at promoting autistic children's language development who are initially language delayed.