I can't see any either. I think an explanation of plural personal nouns in the notes section would be helpful, if/when contributors have time and Duolingo's framework allows for it. I've had a look through the comments on sentences in this lesson, but am still not fully clear when and why you would use 'dobrzy' instead of 'dobre', and 'duzi' instead of 'duże'.
The original sentence has two meanings - it can mean that they are eating them right now (you don't need to add any extra words to mean "right now" because sentence is in present tense) or that good boys in general eat apples (because apples are good!).
Adding extra words just feels unnatural to me, unless you REALLY want to stress it's happening right that moment - adding urgency to the sentence.
You wouldn't say te dobre chłopcy because they are a masculine personal plural noun. It has to be ci dobrzy chłopcy for "these good boys" and tamci dobrzy chłopcy for "those good boys." You would say te dobre dziewczynki, however, for "these good girls," since they're not a masculine personal plural noun.
Actually in this sentence you can have an exception.
"chłopiec" - chłopcy this is regular = ci chłopcy masculine personal
chłopak= te chłopaki/ci chłopacy - we often use "te chłopaki"=not masculine personal.
(many nouns have the "depreciating" form, which is not masculine personal, but with chłopaki it's more common and seen as normal not depreciative)