Cheerios have beta glucan, which is an ideal fiber for an upset stomach. Because you have starved all night, your glycogen (glucose)reserves need replenishing, your protein needs replenishing, you are dehydrated, so cheerios with milk is ideal. read more
The best thing to eat after a stomach bug is rice - especially brown rice - because it contains protein and carbohydrate and is very unlikely to upset you. I'd steer clear of milk but the cereal could be good for the same reasons as rice - protein and carbs. read more