Hi Photo Aunt.......A "Battery Pack" is an external power source, that you can wear on your belt or over your shoulder which connects directly to your flash, providing you with a lot more power than just the 4 batteries that you have in your flash. Take a look at the link below about the Canon power pack. There are more expensive ones out there, but this has worked just fine for me for the past couple of years. You can also do a search on "You Tube", which will show you how it works.
http://www.bhphotovideo.com/c/product/498738-REG/Canon_1947B001_CP_E4_Compact_Battery_Pack.html
You may want to consider buying a Battery Pack for the flash. It will help the flash unit charge a little quicker, but the flash is still going to need time to rechage. Also, you can burn out a flash by not giving it time to cool down.
twoody........Take a look at some of these ideas from MPIX.
Bob
Hi Susie,
All the previous suggestions are great. You might also want to be careful how short your DOF is, since you are shooting multiple people, part of them can get a little soft (Blurry), so you might want to shoot at around f/5.6. I would also try to keep your shutter speed up, just in case there is some movement from the kids.
Anything that I can learn about Photoshop would be great. I currently use CS5.