I looked up the rates at the drop-in daycare that we use for DS, and surprisingly, for 2 kids it's incredibly reasonable.
I saw Friend today and basically said "I'm sorry I couldn't help out watching the kids, but I wanted to let you know about Cool Daycare." I told him their rates, how convenient their drop-in system is, and how much fun my DS has there. Friend seemed happy and said that he would look into that.
Chances are good that he'll use Cool Daycare next time he needs childcare. And, if he asks again I would be comfortable saying "I'm not sure I can handle all three of them alone, have you tried Cool Daycare?"