code: def get_child_values(parent, names):
          
          vals = []
          for name in names:
              if parent.hasElement(name):
                  vals.append(XmlHelper.as_value(parent.getElement(name)))
              else:
                  vals.append(np.nan)
          return vals
docs: return a list of values for the specified child fields. If field not in Element then replace with nan.