def children_to_string(line_prefix = "", s = "")
      @children.each do |child|
        s << child.to_string(line_prefix) << $/
      end
      
      return s
    end
def children_to_string(line_prefix = "", s = "")
      @children.each do |child|
        s << child.to_string(line_prefix) << $/
      end
      
      return s
    end
Returns a string representation of the children tags.

 _linePrefix_:: A prefix to insert before every line.
 _s_:: a String that receives the string representation

 TODO: break up long lines using the backslash