How do I not show purchased books?

I share my iTunes account between my iPhone, my daughters iPhone and my sons iPad. This is so I can buy one app and use on all devices. However I sometimes buy some books off iBooks store and there books that I don't want the kids to access, not that kind! Thrillers, true stories etc.

I've noticed on their iDevices that there is a "purchased books" section with links to the books I've bought. Is rather they not be shown in this section at all. Is this possible? Or what can I do in this situation?

Cheers.