Supposedly he stared blankly in front of him, lit a cigarette and took a deep draught and said "There are always casualties in war" and didn't speak to anyone for the rest of the day.

EDIT: I seem to have recollected this wrongly and mixed it up with a statement later on, but here is the primary source, his personal bodyguard

[His initial Reaction was one of shock. He didn't say anything;he just looked at Jiang and Ye. The two hung their heads in silence;they knew better than repeat the news to him of offer him sympathy.

Mao then blinked, slowly turning his eyes away from them towards a pack of cigarettes on the tea table. He picked up the pack and tried to take out a cigarette but he couldn't do it; he tried again, and again he failed. I hurried over and lighted it for him.

The room was silent except for the hissing sound which as made as he exhaled he cigarette smoke between his teeth. Then i noticed his eyes had suddenly turned red and moist around the rims, caused perhaps by some stray cigarette smoke, or by memories flooding his mind.](https://books.google.ca/books?id=jZswaD6v5AsC&pg=PA153&lpg=PA153&dq=mao+anying+news+reacting&source=bl&ots=1sk-pn2NX5&sig=6zK97zlqXnujCw2knBfBj8V9juk&hl=en&sa=X&ved=0ahUKEwjTh9aIyZfMAhVokIMKHZl5CE0Q6AEILDAD#v=onepage&q&f=false)

A Red Guard Publication(1976)

"In war there must be sacrifice. Without sacrifices there will be no victory. To sacrifice my son or other people's sons are just the same. There are no parents in the world who do not treasure their children. But please do not feel sad on my behalf, because this is something entirely unpredictable".

At the time it was used to show that even sons of leaders are not spared from their revolutionary duty, but more recently it's used to show Mao's views on human life, that he accepted sacrificing them for results.