The $5 million gift toward a new Mill River Park, pledged this week by Steven and Alexandra Cohen, is awe-inspiring. There’s no other way to put it. The money will pay for an interactive fountain/outdoor ice skating rink in the park, plus long-term maintenance and a fund to subsidize admission, lessons and skate rentals for disadvantaged children. The emphasis on children and children’s health is in keeping with the mission of the Steven A. and Alexandra M. Cohen Foundation.