It's funny that babies sleep with their eyes open, but if it happens all the time, you should take this seriously. The most essential reason to give rise to this situation is babies eyes are too big or their eyelids are too short. While they are sleeping, the muscles around eyes are absolutely relaxed and their eyes will open naturally. Besides, there are also some diseases that will stem from this problem. The open eyes is quite a normal phenomenon in babies. However, it will get the invisible bacterium easily which will be bad for the eyes. The next day the eyes may get infection and dryness. Therefore, for the sake of your babies health, you'd better ask a professional ophthalmologist for some advice.