The problem challenges the claim that every wrong must make a particular person worse off. Possible responses appeal to rights, noncomparative harms, duties to provide decent conditions, or the value of outcomes. Each response needs care: explaining a wrong should not imply that the people who now exist lack value or should regret existing.
An invented planning decision changes migration patterns and eventually which children are born. The resulting children inherit poor public infrastructure, although their lives are worth living. Instead of asking only whether they are worse off than they otherwise would have been, ask whether the planners fulfilled a duty to provide decent conditions. That proposal may explain the wrong, but it needs a defended standard and an account of how demanding the duty is for present people.