Sugar and artificial foods aren’t good for anyone-people or animals. Personally I would use it as a very occasional treat, and use healthier things that they love such as vegetables. Also as mentioned before, they do swell up and could hurt the ducks. Either way, you should only feed a few occasionally, but this is just my opinion. I don’t even have ducks yet but this is what I plan to do. Good luck!
Cherrios actually don't swell up they get soggy and wth acid to break down feed works great..Put some Cherrios in water and they become rather slimy quickly..