Triadic joint attention (JA) refers to the shared focus of a child and an interlocutor on an object or event, accompanied by mutual awareness of this shared attention. Although JA is associated with early social interaction and later language development, its definitions and behavioral markers vary across studies and are often restricted to gaze and vocalizations, overlooking other communicative modalities. This longitudinal study followed 14 Swedish child-parent dyads during free play from 9 months to 3 years of age. Interactions were analyzed at both group and dyad levels. Vocal/verbal behavior, gesture, gaze, touch, and facial expression were annotated in detail. Time spent in JA was calculated across ages, and sequential analyses using odds ratios were conducted to examine how specific behaviors predicted the onset of JA. Joint attention increased steadily with age, accounting for 76% of interaction time at the group level by 3 years. Substantial variability was observed between dyads. Across ages, gaze combined with object-directed action, neutral affect, and close physical proximity were the strongest predictors of JA, although their relative contributions varied across dyads. These findings highlight the importance of multimodal analyses and attention to individual variability for understanding the developmental role of joint attention. The methodological approach, time-window sequential analysis, proved effective in identifying both group-level patterns and the diversity between and within dyads’ interactional styles. Moreover, analyses based on age measured in days indicated that age differences – even up to more than one month – played a minor role relative to this variability in dyadic interactional styles.