We probably need more information. I would recommend buying "Storey's Guide to Raising Ducks." What were you feeding them? What did you use for bedding? How old were they? Where did you keep them? Did you have a light over them? What temperature was it? What kind of water dish did you have?
When they are little you have to keep them warm and slowly start reducing the temperature as they grow. You should have a lamp up above their brooder. I think the temperature should be around 90 when they first hatch and then slowly start reducing it. I've heard reduce it 5 degrees a week. You want to have a big enough brooder so they can move away from the heat if it gets too hot for them. They should have duck starter to begin with, some people feed them other things, but that has worked for me. If you search duck treats on here there is a wonderful list of things to feed ducks as treats. I'm sure you will get other good advice. Make sure their water dish is not too big, because they can drown in it. I use a dish and then fill it with enough marbles, so they can't get in. Their water dish should be full all the time when they have food in their dish. Some people take the food and water out at night. I don't usually, because I'm afraid they might get hungry. I put towels down on the bottom of the brooder and change it three or four times a day. I wash the towels in the washing machine after rinsing all the duck poo off of them. (it is a pain, but works well)
Then you have to make sure you post lots and lots of pictures on here so we can all enjoy them!!! Have fun!!!