I've been to Disney World every year with my children since they were one and they are now 11 and 12. We never bring anything for them to do in line, as it is not necessary. If you do your home work and use your fast passes, you will not really be standing in line. Also if you do end up standing in some lines Disney does an excellent job of including themes all along the lines that really keep the kids interested. In fact, there have been many times that I have to tell my kids to hurry up and walk because they want to go slow and look at all the stuff in line.
Finally, I have found the lighter you travel the better. By the time you whip out the etch-a-sketch or game boy or whatever then the line is over, or the kids that do have stuff are so involved that they forget to walk or trip. I really do not think your kids will have any problem.
When ever we incounter a short wait, we always just play word games like 50 questions, or talk about our favorite rides or what not. The only exception is the wait for parades or fantasmic. Sometimes you have to steak out a spot rather early for those events and it is nice to have a little book or something. Sometimes I save the spot and I let my husband goof around with the kids untill show time or vice versa.
Have a great time. Your kids will be so engaged.