What you mention is a typical destructive behavior noticed in kids and a tendency of violence/killing which even adults have. Key point here is: will they also eat the bird after killing it? Is the killing done here for the sake of eating ? or for the sake of enjoyment/destruction (whatever other reason).
i spent part of my childhood on a farm. i watched rabbits and pigs being slaughtered. and of course we ate them.
recently our neighbors slaughtered a goat that my kids had seen alive just before, and we all ate it. we also eat the chicken from the kids grandparents village home that they saw being slaughtered there.
kids killing animals for no reason are an exception, as are kids refusing to eat animals that they saw alive.
if they weren't we'd all have become vegetarians centuries or even millennia ago.
(slightly related: it bothers me that some people think kids should be protected from experiencing how meat is produced. if you eat it, you should know where it came from)
What you mention is a typical destructive behavior noticed in kids and a tendency of violence/killing which even adults have. Key point here is: will they also eat the bird after killing it? Is the killing done here for the sake of eating ? or for the sake of enjoyment/destruction (whatever other reason).