Daughter is the only kid not invited to my brothers wedding

I find it hard to believe the bride has zero family members under the age of 18. That seems highly unlikely. With all due respect, it sounds like you feel a certain way about it and you are taking your own personal feelings out on others. It is unfair of you to solely blame the bride (her and your brother have obviously agreed together to the adults only parameter); it is unfair of you to make assumptions about the bride's family (I find it unlikely there are NO family members under the age of 18.. and perhaps there are best friends/close family friends, etc. that have children that are like family to her that are being excluded); it's unfair of you to not take your daughter's feelings into consideration (why should she be forced to attend an adult only event if she would rather have the sleepover YOU planned for her?). And lastly, it's overstepping to chastise your brother for the parameters he has set for HIS wedding. He has every right to create the guestlist of his event, that he is hosting and paying for, however he sees fit. Maybe it's financial. Maybe there are other children on the bride's side that are being excluded. Maybe they have reached capacity at the venue. Maybe he is taking the feelings of his niece into consideration. Or maybe he is wanting to give you a night off as a parent so you can let loose and have fun. Whatever the reason, it's none of your business, as a guest, what led to those decisions. My suggestion would be to stop creating a situation where there is none, respect your brother's decision, and go have a great time celebrating him at his wedding (knowing your daughter is having a great time with her friends).