How to care for a fledgling house wren?

My brother found a fledgling house wren in the backyard in our pool, and now it's in a shoebox with some pine straw, aspen bedding, and a little bowl of water. We've dug up some worms, but I read somewhere that you can grind something up and give it to them. I can't find a little eyedropper, so is there anything else I can use? Thanks :)