I think it's quite clear (even without calculating) that having children is less moral than donating the equivalent number of funds to charity under the average Lesswrong-human morality.

However, if we want to use the word "immoral" and keep its traditional connotations intact, we have to show that having children is less moral than not having children and taking the money you would have spent out of circulation. (And that would be a problem we could realistically be uncertain about)