The touch screen of mobile devices, such as smart phones and tablets, is their primary input mechanism. While designed to be used in conjunction with its output capabilities, eyes-free interaction is also possible and useful on touch screens. One of the several possible techniques for eyes-free interaction is the virtual button method, where the screen is divided into a regular grid of buttons that can be pressed even without looking at the screen.This paper contains an exploratory study about influence factors on this interaction method. Results indicate, that not only the size of the buttons matter, but also the device orientation and user dependent factors, such as the age or general experience with touch screens. By involving small children in the evaluation we can see the validity of this approach even for the youngest users.