They are within there rights,we had this problem where i worked, when we had a swimming gala,the mothers gave there children packed lunches,and they would have a coffee and sit in the cafe eating there own food,i told them to leave as they were taking up tables that other paying clients needed,they argued your case like one mum had bought one coffee whilst 5 children sat around stuffing there faces,and leaving all there rubbish on the tables, i said you wouldnt go to a restuarant and bring your own food would you,snotty mare that she was, fair enjoyed telling to her to leave!!!