I have cats who do this, thank god my children didn't. I've picked up all manner of live mice and rats, plus shrews, voles, hedgehogs, seagulls, rabbits, taken in various stray dogs but dead things I Do Not Do!
I recall passing a poor dead baby fox at the side of the road many years ago. DD2 was in a pushchair so couldn't have been more than 2. She knew that Mummy was in the habit of saving stray and injured amimals so I guess she thought I could help this one.
"Put him in a box, Mummy, put him in a box. Mummy make him better."
I had to explain that he'd gone to sleep forever because he was too poorly to stay alive with us. :(
DD1, a year older, had already learned this. That happened when she found one of our goldfish floating on his side at the top of the tank.
Pressing her palms together and resting her head on them, angel stylee, she told me, "ooooh look, Mummy, fish is sleeping!".