please look at the singular form: l'enfant est un bon élève (the child is a good student).
structure: noun + verb be/être + another noun, defining the first one (+ adjective in front or after).
now, back to plural: the plural of "un " is "des", but when "des" is in front of an adjective, it is changed to "de".
However, "élève(s)" can be used as an adjective as well, so you can also say "les enfants sont bons élèves" or "les enfants sont bonnes élèves".
Neurology is neurology. Children have to learn a massive amount of information, therefore Mother Nature has given them the wholly exceptional ability to process and store information. Sadly, they do not always realise this at the time, they are too busy. But surely it is something to celebrate and look back on. 'Youth is wasted on the young' is a decidedly sour saying, especially as anyone can put their mind to feeling young!
No, what you need to do is determine if it makes sense to interpret the statement as a general one or a specific one. Because there are errors somewhere else does not justify allowing an error here. You cannot make every expression of "les xxx" into a generic statement. Example: "L'essence coûte très cher en France" would be interpreted as "Gasoline is very expensive in France", not "the gasoline", partly because of the nature of the sentence and partly because of the context (in France).
Well for starters, we could actually use "the gasoline" in that example, but you're right, it's preferable without it. "Children are good students," is just as acceptable as, "The children are good students," without any specifics to tell us that we're talking about a specific set of children. There's no error, because the sentence makes sense both ways.
However, true or not, a judgmental statement remains a statement. Yet, if I were to give such a 'general' statement, I would probably phrase it differently so that my counterparts know that "les enfants" are "all children", like: "en général, les enfants sont..." or "les enfants apprennent facilement", for instance.
"Les enfants sont de bons élèves" (without modification or other context) would not be understood as a general statement but as referring to a specific group of children. i.e., the children. To treat it as "children are good students" (instead of "the children"), is on its face a mistaken premise. Let me give an example. Les enfants tiennent mal (or) Les enfants sont sages. Substitute any other adjective or adjectival phrase after être: bêtes, intelligents, noirs, blancs (these cannot be taken as generalized statements just because we say "les enfants"). Or a noun "Les enfants sont des filles", cannot be understood as "Children are girls". Just because the plural French noun "les" + noun may be taken as a general statement does not mean that it will fit in every situation. I certainly agree that in order to be clear, one would add "en général" if you intend to make a broad judgmental statement, knowing that otherwise it would be taken very badly.
You're right, context (again) would clarify whether the speaker is delivering a general statement or not.
"Les enfants sont de bons élèves car leur cerveau est comme une éponge ; mais les adultes sont encore meilleurs car ils ont vraiment envie d'apprendre".
"Children are good students because their brains are like sponges; but adults are even better because they really want to learn."
If we think of 'learners' instead of the more specific 'students', your statement is simply beyond denial. At what point does a child become a student, using the word in broad terms? And how many 'poor students' are simply kids with a disengaged teacher. Adults may envy them but children's brains are like super sponges. We should be so lucky,- just as once we were!
Well, at first, I was going to say that "élèves" is a masculine noun, therefore requiring a masculine adjective, such as "bons." But then I did some research and discovered that the Larousse online dictionary and the Collins Robert hardcopy dictionary both say that "élèves" is both masculine and feminine. It appears that the spelling of this noun does not change according to gender like "enseignant/enseignante." I would think it would be good to report this sentence if it does not accept "bonnes élèves." http://www.larousse.com/en/dictionaries/french-english/%C3%A9l%C3%A8ve/28257
Until about twelve years ago we used the word pupil for a child educated at school and student for an adult studying at university – at least in the UK. You can see this evidenced in legislation e.g. the Education Act 1996. For some reason the word pupil became disgusting to many, ironically including with those in educational vocations who chose to kill the word through abstinence and destroy the precision of student. The French still sensibly retain élevé and étudiant respectively. May I recommend, if you speak English, that you call pupils pupils, because that's what they are and there's nothing wrong with that?