This very young woman wasn't sure if she was being a bad friend so she asked Reddit:
I (22f) am getting married soon. Since my fiancé and I are childfree and because we plan to have alcohol at our wedding, we decided to have a childfree wedding with the age cutoff at 21.
This requirement so far has gone over well with most of our invitees (most of our invitees don’t even have kids anyway so it doesn’t make a difference for them).
I have one friend, “Mel” (20f), that I had to exclude from the wedding. After realizing that pretty much everyone else from the same social circle had been invited except her, she confronted me and demanded to know why she wasn’t invited.
I tried to explain that it wasn’t personal and that I just didn’t want to have to worry about underage drinking going on under my nose on my wedding day.