Unprofessional behavior

Last week I went to shoprite as I was walking in with my kids the cashiers screamed at me saying No under 18 am now confused what does this law really saying according to my understand To sell alcohol to someone under 18 anywhere. ... is not allowed so why were we screamed at how funny that a big franschier like shoprite would do such an unprofessional thing like that please get people who understand English and can read is embarrassing to come across such behavior in a big organization like that.