Translation:The little children are singing, it is touching.
I have a question about the punctuation in this sentence. We often see a comma used in DL French, where it would not be used in English. In this case, there would be (1) two sentences in English separated by a period, (2) the word "and" inserted after the comma, or (3) possibly two phrases separated by a semi-colon. Would formal French writing really use just a comma?
It's in the singular because you're not referring directly to the little children, but rather to their singing, which is singular. Maybe it'll help if you think about the English translation: "The little children sing, it is touching."
So the adjective does not agree with the subject noun, but rather the verb here? Is that what you are saying?
The adjective "touchant" modifies "it". Maybe thinking of it like this helps. "Les enfants chantent. La situation est touchant."
Predicative adjectives are "c'est" are always singular masculine.
It's perfectly fine and sounds more natural in English to use Present Continuous here. If it was marked wrong, there was another mistake.