How large are they? You will have to judge the situation, but if they have landed in a safe area, the mother bird will continue to feed them. Of course, if they are in an area where a cat might find them, you might want to consider taking them in and feeding them. Bugs,worms, that sort of thing. But fresh because they need the liquids.
If you're unsure, then the best thing to do is call a vet or a humane society near you. I drove a baby pigeon 15 miles through traffic to the animal shelter I had called. They took him in.