albern
silly
Childish, foolish, or not serious in a funny or sometimes annoying way.
Seid nicht so albern und hört auf, mit dem Essen zu spielen!
Don't be so silly, and stop playing with your food!

silly
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silly
Childish, foolish, or not serious in a funny or sometimes annoying way.
Seid nicht so albern und hört auf, mit dem Essen zu spielen!
Don't be so silly, and stop playing with your food!

The word family includes the verb 'albern' (to act childishly / fool around) and the noun 'die Albernheit' (silliness / childish behavior).
Hört auf zu albern, das ist eine ernste Situation!
Stop fooling around; this is a serious situation!
'Albern' (silly) can be used not only as an adjective before a noun or with 'sein' (to be), but also as an adverb to describe a verb.
Das ist ein alberner Hut.
That is a silly hat.
The tone of 'albern' (silly) can be affectionate and joking or negative and critical, depending on the situation. The context and the relationship between the speakers are decisive.
Ach, sei doch nicht so albern, das war nur ein Spaß!
Oh, don't be so silly; it was only a joke!
serious
'ernst' and 'albern' both describe how someone behaves or how a situation comes across. 'ernst' fits when someone is calm, matter-of-fact, or not in the mood for joking. 'albern' fits when someone acts childish or foolishly funny. So the contrast is: 'ernst' is about seriousness, while 'albern' is about inappropriate or exaggerated fun.

Der Fahrer macht im Supermarkt alberne Geräusche, und die Kinder lachen laut.
The driver makes silly noises in the supermarket, and the children laugh loudly.
Greta bleibt im Gespräch ernst, weil es um ein wichtiges Problem geht.
Greta stays serious during the conversation because it is about an important problem.