War is hell, and in most cases --if not all---, the nation responding to an aggressor has to take on tactics of the aggressor nation. Morality goes out the window in war.
1} cluster bombs are like land mines, in that they leave non-exploded bombs scattered over terrain and embedded in grass and soil, buildings etc, just waiting for a child to stumble upon the,. Putins war initiated this cluster bombs and with older technology with higher chances of un-exploded smaller bombs scattered over terrain
....." Since the inception of the U.S. Humanitarian Mine Action Program in 1993, and its merging into our overall Conventional Weapons Destruction program in subsequent years, the United States has delivered more than $4.6 billion in aid to help overcome threats from landmines and unexploded ordnance, as well as the ..."
https://www.state.gov/key-topics-office-of-weapons-removal-and-abatement/