Any suggestions for stopping them?
..perhaps they would like some birdseed better that is scattered nearby..? ;)
Other than that..fence the area off and chuck a cat and/or terrier in..that should sort the mice and the sweetcorn out.. ::)
..sorry...there is not much you can do other than provide something else..
Poison or traps.
Had the same problem with sunflowers. I don't bother growing them anymore. :(
Develop a taste for sweetcorn that isn't ridiculously sweet - grow the old-fashioned kind that don't taste like a sugar cube.
Pick them when they have flavour and before they become sugar - mice are like kids - they have "no taste" for the finer things in life.
Cheers.