def move_children_to_parent
      children.each do |c|
        self.parent.children << c
        c.parent = self.parent  # is this necessary?
      end
    end
def move_children_to_parent
      children.each do |c|
        self.parent.children << c
        c.parent = self.parent  # is this necessary?
      end
    end
move all children to the parent node
 !!! need to perform validations here?