A person under the age of 18 years shall be present at the imposition of sentence in cases for violation of chs. 341 to 348 and 351 or ordinances enacted in conformity therewith under ch. 349. This section does not apply to parking violations or to cases where a stipulation of guilt or no contest has been accepted for a violation of a local ordinance. A court may waive the requirement of personal appearance under this section in cases of exceptional hardship.