enforcing age restrictions!!

why are age restrictions not enforced. I am a primary school teacher (Grade 7) and on the occasion that i decide to spoil myself to a movie i generally choose a restricted movie so i dont have to end up in a cinema with children i teach. This evening i went to see Deadpool which has an age restriction of 16. in the cinema were children currently in Grade 7 and some that were in Grade 7 last year (13/ 14 year olds). This spoils the entire evening as as their teacher it makes it difficult for me to relax and enjoy the show knowing how inappropiate the content is for these children. When I reported it to the staff they told me they have no way of knowig how old the children are and cannot really enforce th age restriction. if this is the case what is the purpose of the restriction