Just to be clear, remove the grills before spraying them with anything. You don't want to damage the speakers with cleaning solutions. I hope, however, that this already seems obvious to you. Of course, you will need to keep the two year old out of the room while the grills are off, or you may end up with hands on actual speakers instead of grills.
After cleaning, you might also want to mount the speakers too high for the two year old to reach. Keeping things up high is good when you have little children.