D.M.
M.,
It will never end...you just have to be the bigger person and let it go. Once you've explained your side and the importance of the stuffed animal, your ex should be able to make the mature choice and mail it back. If he hasn't yet, he isn't going to.
I too, have ex issues and to be honest, you are always going to have to be the bigger person. The mature adult, who knows better and makes the appropriate choices for your kids. If I had a nickle for every excuse I heard, I'd be rich!!
Take a special trip with your son to the store and let him pick out a new stuffed toy to be his pal, and then before he goes to his Dad's house again take him to pick out a special 'Daddy visit toy'. I have had to do this with my son, and it's worked pretty well. Don't tell him he can't take 'special things' to Daddy's house because it may create a sense of distrust for his father. And, that may come later anyway, but let him discover and create HIS own opinion of his father...not yours.
I hope this helps...and trust me it doesn't get any better with people who enjoy creating discord in their lives and the lives of others. But, we've got to let it roll off our backs to be the best Mommy we can to our kiddos, even their Daddy's need to check themselves.
Good Luck.
Deanna