I'd stick with the 243. It has a noticeable decrease in kick over the 7mm08. Not a lot of difference for an adult, but the kids will definately feel it.
If your daughter doesn't hunt much, modifying the stock will work, but seeing as you have two granddaughters I'd suggest getting one of the youth, or short stock, rifles out there for them. Get them both the same new gun, and they can't argue over who gets what.
If you have one, a .44 magnum rifle has even less kick. My father has one that I used when I started hunting. I hope to get that rifle someday. It's older than I am, and sometimes passing on an older reliable gun has meaning as well.
I wish the best of luck to you and your family. No matter what you do, I hope everyone has fun.