That's the conclusion of a post by Eric Posner of the University of Chicago:
"Let’s suppose that the sanctions regime had continued for 10 years, from 2003 to 2013, and further that security flattens out—it doesn’t get worse, but it doesn’t get better. Under these assumptions, 400,000 Iraqi children would have died if the war had not occurred and the sanctions regime continued. Now, almost 100,000 Iraqis died during the war, and so one of the war’s benefits is that it saves the lives of 300,000 Iraqis (over 10 years)."