I'm going to prank my little sister and her friends with a scary doll
Why would you prank your sister and her friends like that?
I want to teach her how to take care of creepy dolls.
Intentionally scaring a child can have lingering effects that persist into adulthood.
I don't care, she's just like all children, very fragile. But it's all good since they don't remember.
Of course children can remember things when they become adults. I'm sure you have good and bad memories you still have. Just because you assume someone won't remember doesn't make it okay to do something to them.