Well it is obviously true that the bombs dropped on Hiroshima and Nagasaki were dropped by an ally of Australia. And that they killed tens of thousands of civilians, including children. As a matter of fact, it's hard to say whether the atom bombs killed more people than, say, the Tokyo firestorm. That seems something of a moot point though.

Was it "terrorism"? That depends a lot on how you define terrorism. It's not common to describe bombing of civilian targets in WW2, whether by the allies or the axis as "terrorism" (eg. I can't recall The Blitz ever being explicitly referred to in this way). The way the word is used also often excludes states. Personally I probably would call it a form of terrorism, but this is a consciously political usage.

One thing to note is that Hiroshima was a highly militarised city, with legitimate military targets dispersed around it. Even a conventional bombing campaign to hit these targets would likely have caused devastation to the city.

The really big question is were the bombings justified? For example, was the alternative an invasion of Japan that would have cost many more lives (both civilian and military)? For this I'll have to refer you to the FAQ which has a number of items on the subject.