[Halcyon]

Awwww. I'd love them to be in my garden.
Make them a little shelter out a box and make sure its clearly labelled out so that it doesnt get thrown in the bin.
Give them some water, a few bits of bread, not too much or it will make them ill, and then keep an eye on them. If you can make sure its safe from foxes as they would just swallow them whole.

Then look out for the parents and see if they go off with them.
With it being a built up area with a motorway, I'd say the best thing might be to catch them and take them to the sea, however I dont know enough about ducks to know if they need their parents or not.

Good luck.