If you want kids, you wear one of these. Simple as that.
To add to Ads' comment about Sir Donald Bradman famously wearing one: in his book The Art Of Cricket he points out that they are "confidence producers", and that "If you do (bat without one), I'll defy you not to flinch when a fastish ball ... comes back sharply from the off". He's about right: when you're out on the cricket pitch, it's not a 9-inch ball of between 5.5 and 5.75 oz. It's a missile, aimed right at your head or (worse) your crotch. And it's coming at a hundred miles an hour, sometimes.
Often also called a protector or (less frequently) a cup, these are often made out of a hard plastic and are often white. They come in the same basic shape (yes, that of a gas mask) but all have slight variations. If you're still not sure what it looks like, search the Internet for a video advertising VB and starring Shane Warne - where he "hangs up his box".