1. override
void visitChildren(RenderObjectVisitor visitor)

Calls visitor for each immediate child of this render object.

Override in subclasses with children and call the visitor for each child.

Source

@override
void visitChildren(RenderObjectVisitor visitor) {
  assert(_children.length == rows * columns);
  for (RenderBox child in _children) {
    if (child != null)
      visitor(child);
  }
}