Function route_to_children 

pub fn route_to_children(
    children: &mut [Box<dyn Widget>],
    nodes: &[NodeId],
    event: &WindowEvent,
    ctx: &mut EventCtx<'_>,
)

Route event through a container’s children, first handler wins. A child latching a drag gets it exclusively, so the drag survives the cursor crossing a peer that would claim it first; a child holding an open modal owns input the same way.