Daughter wearing heels

My fiancé and I are getting married in June and our daughter is in the wedding. She is 12 years old and wants to wear heels to the event. My fiancé does not want her in heels because he thinks it's too mature and wants her in flats because it will be more comfortable for her throughout the night. Her dress is floor length and he doesn't want her wearing heels running around with the other kids and getting hurt. Any opinions?