What can I sue for if the a manager didn’t accept a coupon for my child since our last names didn’t match?

I sign my children up for birthday clubs and periodically receive emailed coupons for restaurants. A few days ago, we went to a restaurant to eat and had a birthday coupon to use for my daughter on her 5th birthday. The manager was called to approve the coupon. When she came over the first employee helping us asked her, how coupon was approved for a minor child with no ID. The manager told her to ask for the parent’s ID. My email address was on the paper with my full name. After looking at my ID, the manager then told me that he can’t take the coupon because my child and my last name don’t match. I asked her what difference it made when she is a minor and I am her mother and that is why I receive emails for my children. I also asked her where it was stated on the paper. I have called corporate and I am waiting for a return call. My family was very upset and left the restaurant. My children were crying and didn’t understand why we were treated so poorly and humiliated in front of staff, customers and the rest of our family. They had come to celebrate her birthday with us. I didn’t care about using the coupon but on the coupon it definitely doesn’t say that a child and mother last names must be the same. In that case, I would not been able to sign her up and we have used them in the past. We could not stay after we were discriminated against and I will not let this rest until the matter is resolved!