Learn Hardcore German: Zwanzig Kinder spielen im Park.

In German, cardinal numbers (like zwanzig) function as determiners and normally replace the need for an article. You simply say zwanzig Kinder to mean “twenty children” in an indefinite sense. (If you wanted to specify “the twenty children,” you would add die: Die zwanzig Kinder.)

Why doesn’t zwanzig get an adjective ending (e.g. zwanzige Kinder)?

Cardinal numbers aren’t adjectives in German; they act like their own category of determiner and don’t take adjective endings. They remain unchanged regardless of the noun’s gender, number, or case.

Why is im Park used instead of in dem Park?

im is simply the contracted form of in dem. Since Park is masculine and you’re indicating location (answering “wo?”), in takes the dative case (dem Park), which is routinely shortened to im Park.

What case is im Park, and how can I tell?

It’s dative singular. You can recognize the dative because the article would be dem (contracted to im). Location prepositions like in require dative when no movement/change of place is involved.

Why does the verb spielen end in -en rather than -t, as in some other forms?