Honestly, I'm torn because I wouldn't want any animals to come to harm either, but I was really into bugs/ frogs/ toads/ snakes/ salamanders, etc when I was small. I know I did injure a few inadvertently- and it's a hard lesson to learn as a kid, but an even harder for the animal to endure.
I am the person I am today, vegetarian and very peaceful because as a child I was allowed, encouraged and borderline obsessed with the animal life I encountered. For the most part I watched them and interacted for a while and returned them to their natural settings, but I think If I had just observed them in nature without interacting with them I would never have developed the compassion and interest I have in nature- I think I needed to experience holding the animal, watching it's reaction to me, it's actions, feeling in the case of small reptiles, amphibians and the like their little hearts beating, just seeing their uniqueness and to experience they are just as alive and aware as myself. I learned to appreciate them as individuals which is a huge part of growing to respect animal life I believe. I could(more on this later) identify 15 toads from our yard specifically based on their markings and the pattern of their "warts".
At the same time there are LOADS of things I would do differently while teaching my own child. I think if my child wanted to do as I did one summer, and keep a terrarium of toads to observe for a month or so, I would teach my child how to build a very appropriate environment- probably make it into a real project for them and build it from scratch, create a natural living space for them, harvest or purchase food for them so that they would benefit from being observed with great stores of fat in time for fall and I would explain all of this to them. My parents on the other hand, knowing I was gentle let me keep them in a big rubber maid tote without a top with some ground and rocks but nothing spectacular for sure and definitely not a great place to keep 15 toads for a summer, though luckily I was vigilant enough not to harm any and none died and I was able to release them all later into the yard.
If my child showed and interest in ladybugs we would research them completely and perhaps build a small temporary shelter for them to observe overnight.
I think it's important for children to experience other creatures on their terms because someday, as I did, they will begin to see that animals become stressed from capture, and they get scared and perhaps observation, or just holding the creature for a moment then releasing them back to where they came from is the most humane choice. You can read all the textbooks in the world about an animal but for me until you experience that creature one on one there is no real connection.
I think a great compromise is education, brief observation and extremely supervised longer term observation and then plenty of contact with domestic companion animals of many varieties is the best way to cultivate the understanding and passion for animals.
I think a butterfly project would be OK in classroom as long as the children were not allowed to touch the (proper and comfortable) enclosure, educated greatly and then the (environmentally appropriate) butterflies were allowed to strengthen and acclimatize and a short field trip was taken to release them in a field or a wooded area away from prying hands.
just MHO..... Definitely not an expert or the gospel, lol.