Not sure what species you would be thinking of...? Perhaps share what the point is that your segment is trying to make? Non-native species generally compete with, displace, eat, or harbor diseases &/or parasites that can or do compromise native species, thus my confusion. Happy to chat more on this.

Thank you for the clarification. There's a contested body of thought often called, "novel ecosystems," in which I think this idea of "non-native but not invasive" might (?) be rooted. A lovely summary, including citations of key works, appears here https://www.britishecologicalsociety.org/content/novel-ecosystems-the-new-normal/ and might be a great resource in which to anchor a class research-and-debate type of activity. 
And/but particularly for young learners and future citizens, as an ecologist I would be really hesitant to unintentionally imply that further non-native releases are "not harmful". We (global efforts to conserve native species, even the "common" ones) are desperately losing native species, including to domesticated cats, for example - because folks cling very, very hard to the idea that non-natives can play "ecosystem roles" when really, out of their native ranges, the prey have ZERO defenses against species-obliterating losses.
I hope this is helpful :) It would be truly wonderful if you decide to even introduce your 6th graders to the British Ecological Society's site so they know there are national and international bodies of scientists learning about and informing management of lots of cool organisms and systems!!