Remove all their children from this render object's child list.
More efficient than removing them individually.
Source
void removeAll() {
ChildType child = _firstChild;
while (child != null) {
final ParentDataType childParentData = child.parentData;
ChildType next = childParentData.nextSibling;
childParentData.previousSibling = null;
childParentData.nextSibling = null;
dropChild(child);
child = next;
}
_firstChild = null;
_lastChild = null;
_childCount = 0;
}