Learn Polish: Na Wielkanoc malujemy jajka.

When talking about doing an activity during a holiday or festival, Polish typically uses na followed by the accusative case. You will also see this in phrases like na Boże Narodzenie (at Christmas).

If na takes the accusative case here, why does Wielkanoc not change its ending?

Wielkanoc is a feminine noun that ends in a consonant, just like its root word noc (night). For these specific feminine nouns, the accusative form is identical to the nominative form, so no ending is added.

Why is the imperfective verb malujemy used here rather than a perfective verb?

The sentence is stating a general, repeated tradition. Because painting eggs happens every year as an ongoing custom, the imperfective aspect is required. If you were talking about completing the task of painting eggs this specific upcoming Easter, you would use the perfective pomalujemy.

I have heard the word pisanki for Easter eggs. Why does this sentence use jajka?

Pisanki is indeed the word for the finished, decorated Easter eggs. However, the phrase malujemy jajka focuses on the raw material and the action: you take regular eggs (jajka) and paint them, which is the process that turns them into pisanki.