Learn Dutch: Waarom gaf de oppas ons een schattige kleine groene cactus? - Why did the babysitter give us a cute little green cactus?

Just like in English, Dutch organizes multiple adjectives in a specific hierarchy. Subjective opinions like schattige (cute) come first. These are followed by objective physical traits, where size (kleine) generally precedes color (groene).

Why do all three adjectives get an -e ending here even though they follow the indefinite article een?

Because cactus is a de-word (de cactus). Adjectives modifying a de-word always get an -e ending, even after een. They would only drop the -e if they were modifying a het-word after een (for example: een schattig klein groen plantje).

Why is the indirect object ons placed right after de oppas rather than after the cactus?

When the indirect object is a pronoun like ons (us), it strongly prefers to sit as early as possible in the middle of the sentence. It comes right after the subject (de oppas), well before the long direct object (een schattige kleine groene cactus).

How do we know the gender of de oppas (the babysitter) in this sentence?