I agree with John, the first thing to remember is this isn't an audition. Your audience is already predisposed to like you, and they want to hear from you.
What I did (when I was invited to talk for WCDR and got to meet the fab Mr. KTC) was first start off talking a bit about my road to publication, as I was talking to other authors and I knew they would be interested, and then I tried to introduce a few new ideas that maybe they hadn't thought of. I explained why I liked Children's literature so much, discussed the importance of humour in books in general.
The reason why I said what I said was because they had invited me to speak to authors about writing for kids. They don't get a lot of kid's book authors, so I wanted to share some ideas that were unique to the genre.
Now you say that everyone is talking about home school stuff. I'm not really sure what that means to be honest, but I am sure that could be a place to start. And what is the nature of the convention, what is it, and who will be attending? Ask yourself why you were invited (and don't go all modest and say "I don't know! I'm just little ol' me!". The biggest thing I've learned is that it is unfair to get so modest when people have gone out of their way to express an interest in having you speak. It's disrespectful in my mind. Though yes it is difficult to wrap your head around the idea of others wanting to hear from you). So, why do you think they wanted you specifically to come? And you know what, you could even ask them that question, and what they would be interested in hearing you talk about. I've been on several panels now, and have spoken several times to schools etc (only once to that group of grown ups though, and it was so cool), and every single time I have asked the person who invited me, what sort of thing they think their audience would want to hear.
You can so do it! And I know it's a bit cheeky to do this, but as I am also an actress, have been a teacher and know a fair bit about public speaking, so I wrote a 4 part series on Speaking Aloud on my blog several months back. If you want to check it out, please visit this
link, and then just click on "newer post" to get to each subsequent posting. It's more to do with reading aloud from one's book, but there is some general advice in there about presentation technique, specifically
here. Only if you are interested of course.