My husbands brother sent a 'bull dog' from Jacksonville a few years back for my husband....when we got home our little boy was leading it around on a string.
Bingo as he was to later to be named was a fiest at best with a little terrier mixed in for tenacity. He was horrible, every chance he got the little 'stard would pick a fight so we had him fixed to see if it would slow hom down....

yeah right.
I came home one day and Bingo starts smack with Charlie right at my feet....I let them fight it out for a few then proceeded with the hot shot to break them up. When the little one got home I proceeded to tell him that Bingo HAD to go. Well he started bawling and all I could see was this blue eyed little darling and this little feist dog running and playing in the yard......so we sent him to live at his nannies house

now he gets to visit on weekends!
He hasnt gotten attached to any of our other dogs since, he plays with them but he understands the concept of they have to earn their keep and that they may or may not come home. We do not hide any form of death from him, its a normal part of life that I think alot of people refuse to deal with.