Subjects and predicates for eight-year olds

My eight-year old son goes to Japanese school every Saturday morning during the school year, and over the summer, he has some homework to do. The other day he showed me a question that he didn't understand:
「次の文の主語とじゅつ語をかきましょう。」(i.e., Write the subject and the predicate of the following sentence.)

This gave us an opportunity to talk about how to identify a subject in English and in Japanese, during which, he told me they'd been learning about verbs and adverbs at "English school" (the local elementary school).

I wasn't sure how far to go with these topics, so I kept them fairly basic, telling him that the subject usually comes before the verb, and it's usually the person or thing doing the action: pretty traditional, but good enough for now. Notice the hedges in there. I was even less sure with predicate, because I wasn't really sure how close the Japanese notion of じゅつ語 is to the English notion of predicate, and I also wasn't sure what his teacher had told him. Luckily, the sentence was 多くの花が咲いている。(i.e., Many flowers are blooming.), so the predicate was obviously just 咲いている (i.e., are blooming).

I'm glad to see these topics coming up in school, and also glad to have a chance to talk about them with my kids. I wonder when subjects and predicates will come up in "English school".