This fails to fit the spirit of the problem, because it takes the preferences of currently living beings (the childless couple) into account.

A scenario that would capture the spirit of the problem is:

"Eve kills a moderately happy hermit who moderately prefers being alive, uses the money to create a child who is predisposed to be extremely happy as a hermit. She leaves the child on the island to live life as an extremely happy hermit who extremely prefers being alive." (The "hermit" portion of the problem is unnecessary now - you can replace hermit with "family" or "society" if you want.)

Compare with...

"Eve must choose between creating a moderately happy hermit who moderately prefers being alive OR an extremely happy hermit who extremely prefers being alive." (Again, hermit / family / society are interchangeable)

and

"Eve must choose between kliling a moderately happy hermit who moderately prefers being alive OR killing an extremely happy hermit who extremely prefers being alive."