Feeding Ducklings - help!

Hi all. At the school where I work we have a couple of little ponds and the last few years Mallards have come to breed. Great to see all the little ducklings. The technology people have built duck houses and one of the teachers has put ramps down for them to get in and out of the water and also feeds them. Unfortunately she has problems with aged parent care and has had to take a few days off. I'm happy to take on feeding duties but not sure what's best to give them. I know bread is wrong but just read an article suggesting defrosted frozen peas and/or oats. Are these suitable for little ones too please? Or if not, what? There is probably special duck food you can get from specialist shops but I don't know of any such outlets though plenty of supermarkets and regular pet food shops nearby. Advice welcome please.