Gait initiation (GI) requires precise postural control facilitated by anticipatory postural adjustments (APAs). Although previous studies have investigated APA development, few have examined the modulation of APAs and margin of stability (MoS) during the complex task of obstacle crossing during GI (GIObs), particularly comparing children and adults. This study determines how children and adults modulate APAs and the MoS during GI, with and without obstacles. The participants included 56 typically developing children (3–16 years) and 20 healthy young adults (19–24 years). The obstacle was placed at a distance equivalent to 50 % of the first step length of the participant, and its height was set to 10 % of the leg length. Kinematic and force plate data were collected to calculate the APA onset (APAonset) and peak (APApeak) in the anteroposterior (AP) and mediolateral (ML) directions and MoS in both directions. Children exhibited delayed APAonset and larger APApeak values than adults. Adults exhibited a greater decrease in MoS_AP during GIObs than during GI, whereas children maintained a significantly larger MoS_ML during GIObs. The step length was longer in GIObs than in GI, with no significant difference in clearance height between the groups. Compared with adults, children exhibited delayed APA onset, higher APA amplitude, and larger MoS_ML during GIObs, indicating a more conservative approach to enhance lateral stability, possibly reflecting an adaptive strategy that aligns with their developing neuromotor control. These findings contribute to understanding the developmental trajectory of dynamic balance control and can inform age-appropriate interventions to support balance control in pediatric populations.