I started out wanting to be a teacher. I have my degree but have since discovered magic and entertaining lay-folk is my main job now and I love it. I still do however sub in the local schools as my part time job to magic. I am certified to sub at any age level. I smiled when I saw this post because I use magic all the time as a sub and like you said it can help keep the kids "good" if they know they are behaving to see a trick aka get entertained by the adult in the room.
To the tricks:
-Try Pointless by Gregery Wilson
-I know you have spongeballs but they do play well for younger kids like you have
-I do what I think is called the Bird Catcher Paddle (Penguin sells it and Jay Noblezada teaches the instant lesson when you order it)
-Rope magic like prof nightmare/Richard Sanders' rope dvd has more moves on it
-Airborne with the greatest of ease when you pour yourself a drink will really grab their attention.
If you need more let me know and ill respond. have a good one, teach!!