You may censor anything you wish IN YOUR OWN HOME, please keep your hands off your hosts’ things, or don’t go there for a visit. It sounds like they had some fashion magazines in their bathroom. If you were bothered by it, you should cover it with a towel while your kids are using the bathroom. I presume you are a grownup and know what women’s underwear or shortsleeved clothing look like. It might not be your or MY first choice for bathroom reading (and personally I do not think it belongs in the bathroom), but this is not your house, and there is no way to tell your hosts that they have offensive (to you) material in the bathroom, without being…well… offensive.
Sorry, but I am really trying to be objective here. Not all people will think or act as you do, but you still have to respect their boundaries in their own homes. If the magazines present there were published by Mr. Hefner, however, that’s an entirely different matter, and I would have no problem bringing a copy of said magazine from the bathroom to my host and mentioning that my kids asked me about it. I am fairly certain, he would be a little abashed and remove the item(s) in question with all due alacrity.