The poor little things, how can people be so cruel as to dump them like that. Well done on the rescue!!! You're like a ducky super-hero :)
Laying feed has too much calcium for growing ducks - so wait another 4 months before giving them that. For now, get some pullet grower for them and a niacin supplement. Or you can use gamebird maintanence feed. The two things to look for in feed are that the feed is suitable for birds that are not laying and also that the feed has less than 18% protein (ideally about 15-16%). You can feed them this kind of feed for the next 4 months, then they can go on layer food.
They will also enjoy fresh greens (e.g. any leafy greens) and thawed frozen peas. A good range of fresh greens is a great way to supplement their diet in a healthy way. They will also like young grass cut up small and put in a bowl of water. They will need a water dish that is deeper than the water you have in the bath. They need to be able to put their faces in it to clear out their nostrils. Just something as deep as the length of their head and bill combined. Doesn't need to be wide, just something they can't tip over.
As far as age goes, I'd say maybe 4 weeks??
What colour are they? Not sure if you have a Fawn and White runner there or just a face covered in food! LOL.