Feeding Ducklings:How much starter crumbs do you give?

We just had a little flock of 6 abandoned ducklings. Since they were two days old, we fed them chopped spinach/grated carrots/and mashed boiled yolk til we were able to get a sack of Duckling Starter Crumbs. Since then, we fill the bottom of a small plate (8 1/2 cm diameter exactly). and feed them every day (often emptying and refilling once they get wet or soiled every two hours or so). But something struck us and made us realise what on earth we were doing was pretty reckless and rather stupid. We have no idea how much exactly to give as their daily portions. We know we should switch to pellets after 3-4 weeks, but the bag doesn't explain anything else. So we were hoping if someone here knows and can lend a hand in this dellimma. So far the ducklings seem fine, and they're now bigger and look very much like a normal 1-week old duck now. So far it feels like they're doing okay, still, we hope to know more on what we're doing. Thanks for the help!