I don't know if this is true for other countries, but most 5ths graders here already know every swear word that you can expect to find on zk (People know the swear words, but they don't use it every 3rd word. So don't go "Kids these days..."). So you probably don't need to worry about kids learning swear words from zk.
also, What's the swear word situation like where you live?