If it is cloth type material, you can use stain remover such as Resolve. You can also use bleach and scrub it with an old toothbrush. Depending on the type of shoe you can throw it in the washing machine. If it is on rubber, you can use a Clorox wipe or Magic Eraser.
You could try white nail polish I guess... and also try bleaching them ( With an adults help of course). Other than that, I don't think there's anyway, because white holds stains. Sorry about your shoes, that's messed up!
Nail polish and a q-tip always works for me!
try WD 40 but spot check it to make sure it doesnt discolor your shoe