My children came equipped with a sibling detector, and I don't know how to disable it. If I so much as think about getting cuddly with my husband, one of the pair shows up whiney and in need of something.
I'm quite certain that they are actively trying to prevent a younger sibling (I asked the 4yo if his alarm was going off after he appeared at midnight crying. His answer- "My alarm was going off lots!"). They also show up if we talk about going away for a weekend or out to dinner without them.
I have no doubt that my children possess an extra sense related to my love life. Their success rate is much to high to be coincidence (I'm tempted to start tracking it for statistical purposes), and they are driving us batty. Maybe foil hats would work.