Nothing can ruin a day of watersporting like getting a rash from water abrasion. When you are taking your kids out on the water having a rash guard can save them and you a great deal of pain and inconvenience. If your kids are surfing, kayaking, waterskiing, tubing, or any other activity that is fun and awesome on the water you want to do everything to make sure that they not only remain safe but have as great a time as possible.
Rash guards are also called rashies in some circles, especially in Australia. I think that name sounds too much like an unpleasant candy. But I digress, the point is that rash guards are so popular in Australia that they have earned a cutesy nickname, and Australia is full of some of the most dangerous animals in the world, so rash guards are inherently more badass. I met a group of punk rock Aussies once and they told me that there is a bird in their country that shoots poisonous barbs from its wings. Crazy.