I have four animals that are my principle models.  All four are OOAK's--One of a kind.  They were hand made, mostly in Eastern Europe, and make much better models than actual animals, or kids for that matter.  They cooperate, hold still, and require minimal payment. 
The first to arrive was Jasper, the rabbit, who was an absolutely amazing birthday present.  Then came Charles, the bear.  After those two got along so fabulously, I added Duchess, the small dog, and finally we have Abe, the mouse.  Abe is new and not in many photographs yet, but his time is coming soon. 
There are even rumors of a children's book, but don't tell them or they will increase their demands.  As it is, they are very good at hiding covertly in my bag until the coast is clear, then they hop out, we snag a bunch of pictures, and some of them are even good!  Then they jump back in the bag, and home we go.  During their down time they like to play cards and eat popcorn while debating the merits of wool versus cotton sweaters!