I've taught kindergarten and first grade for a number of years, so I think I can give you a few suggestions...
I'm picturing you as a guest speaker in front of multiple classes - is this correct? Usually, this would happen in the gym, cafeteria, or with lots of small kids crammed into a classroom.
For a general theme to the presentation, I'd tell about storytelling, types of stories, importance of stories, using the imagination, perhaps the physical/mechanical explanation of how books are made (printing, binding, how many of yours have been made, maybe how they're transported to book stores and sold online). Another big theme is obviously the importance of reading, and how much fun it is!
Young students always enjoy a Powerpoint presentation (you get to turn the lights out and that means FUN!). Include silly graphics, noises, pictures from your books - limit to 5-7 minutes.
For an activity or two - perhaps to break up the sitting - I'd think about teaching a little song and some actions to go along with it. Also, it would be nice if you had something to give to each student - like a coloring page, or a bookmark.
For a 30-45 minute presentation, you should plan on doing 5-6 different things - talking, showing, singing, Q&A, more talking, more singing...I know it sounds like a lot, but little kids can only pay attention to one thing for very short amounts of time.
And even though it sounds like fun, I wouldn't suggest an art project with lots of small kids. The space, supplies, and available help might make it tough. Everything that you plan on doing, you should plan to facilitate - don't count on any supplies, desks, set-up, etc. This makes it simpler for everyone, and means you're ready to go anywhere!
Hope this helps! If you have specific questions, please let me know. I'm happy to answer.