Not a native english speaker, but this seems like a nitpicky non-issue to me. How is it not the same as "could you please pass me a glass of water" vs. "would you please pass me a glass of water"? Both indicate a request rather than talking about actual physical ability to perform the action.
Also, I would agree more with your point if the parent said "It could be great if this could be done..." instead of "It would be great if this could be done". The first "would" seems to indicate to me pretty clearly that the parent was talking about a request rather than ability.
Also, I would agree more with your point if the parent said "It could be great if this could be done..." instead of "It would be great if this could be done". The first "would" seems to indicate to me pretty clearly that the parent was talking about a request rather than ability.