Is he positive they were abandoned? Is it possible momma cat had just gone to find herself some food?
Please have him go back and see if he can see the mom around. She will be frantic looking for her babies.
This site gives you step by step instructions and how much babies should get fed. It is more concise than I could hope to be...
http://cats.about.com/cs/kittencare/ht/bottlefeed.htm