We sold our house when our kids were 3 y.o and 8 mos, and I feel your pain! We put a bunch of stuff neatly in boxes in the basement, and when prospective buyers would come over, I stashed just about every toy that couldn't be neatly "displayed" in a proper place (like my daughter's room), in an out-of-the-way place. You have to think of places where people aren't going to look (like they will look in the closets, so you don't want to clutter them up). We used behind the sofa and under the beds, aside from the basement. We also tend to live with a lot of clutter, but I knew that having our house be super neat could be the difference between more $ and less, so I really knocked myself out. (p.s. It worked--there was a bidding war on our house and we ended up getting enough money to almost totally support ourselves while we went overseas for six months. Of course, then we moved to a much more expensive city, and we are despairing of ever owning again. sigh....).
We read lots of library books, and I would change the wording so that they were more positive than some of them were (I didn't want to really put the thought of "I don't want to move" into dd's head!). I'm sorry I can't remember one specifically. BUT, I will say that we got professional packers and it was one of the best things we've ever done. Seriously, it's like hospice care for your house--it lets you fully live in it until the day you move. In one day, the movers came in (we had packed nothing), packed our four bedroom house, and loaded it on a truck. It was great, esp. for our dd who didn't have to deal with weeks of boxes and her toys being put away.
Good luck with it all!
Mama to four great girls: 14 , 12 , 7 and 4