Jennifer,
I wrote my first press release in May and submitted it to PRWeb. Like you, I wasn't too impressed with my effort, but the PRWeb editorial board gave it a 5 out of 5... wooohooo!
Here's a link if you want to model the format and flow.
http://www.prweb.com/releases/2005/5/prweb241034.htm
Sometimes, the best headline and lead are buried a few lines into a piece. In your case, I think "Adventures in Kidland, Mississippi Style" is a better headline. It's more interesting than --- another website. It shows why you're unique.
I'd also punch up the close a bit -
Put this sentence somewhere in the body, "The web site accepts submissions from event coordinators, individuals, and park commissions."
And close with, "To list your event, send sumbissions to Jennifer at ..."
Add details to bring it alive: what places, which events, what parks? Name them.
This seems a great site. My kids are teens now, but I could have used something like this on a sunny Saturday in New Hampshire.