What with all this rain, there has certainly been some mud around lately hasn’t there? If you are lucky enough to work in a school which is near a muddy track why don’t you take your class and invite them to see if they can deduce who has been there before? A lot of science involves trying to work out the whole picture from a limited amount of evidence. Astronomers, for example, use faint patterns of light to work out what is in outer space; forensic scientists examine the scene of a crime to ascertain ‘who dunnit’ and geologists and paleontologists find evidence of what happened many thousands of years ago from traces left behind.
If you are unable to take your class to a muddy track perhaps you could take some photographs to show them and then challenge them to take photographs of their own when they are at home? Perhaps they could share them on the school website and challenge others to work out what has happened?