Tex,
1) If you are going to pay for the worms,......DON'T!! Talk to local golf courses & tell them you will mention them if they allow some of your volunteers to collect nightcrawlers from their freshly watered fairways.
2) For those children who easily tire of fishing, have plenty of copies of the "Let's Go Fishing" section from Field & Streams' Anniversary issue for them to work on & enjoy. (see JC's article).
3) When are you having it? I make a pretty darn good peanut butter fudge, most kids have a sweet tooth, & if I have a little advance notice, I would LOVE to make a donation of 5 or 6 pounds of "kids' health food"!!
Mike