What's this doing there?!

I'm not sure if it's meant to annoy me or out of honest confusion, but my kids seem to think taking my bookmark out of my books is absolutely necessary. Either they think it's funny, they are annoyed by my reading and want me to stop, or they're wondering why there is a little piece of paper in Mommy's book and feel that they are helping me by removing it. Whatever the reasoning in their 3 and 1 year old minds, it's annoying. Luckily, I'm only a few pages into this book, so it is easy to find my place at the moment. Slightly more annoying when I'm halfway through the book.