This is the earliest known reference in the Dutch press to Mozart’s death. The Ommelander Courant was a regional newspaper founded in Oct 1787 and published by Leonard Bolt (1760–1806) in Hoogkerk, in the province of Groningen (the Netherlands). The newspaper appeared on Tuesdays and Fridays.
The notice transcribed here seems to echo the report in the Pressburger Zeitung of 21 Dec 1791, which also suggested incorrectly that Mozart had only one son:
Für die Wittwe des verstorbenen Hrn. Kapellmeisters Mozart ist auch gesorgt. Se. Maj. der Kaiser haben ihr den ganzen Gehalt ihres Mannes gelassen, und ihren Sohn hat der Baron van Swieten in Versorgung genommen. [Dokumente, 375]
The widow of the deceased Kapellmeister Mozart has also been provided for. His Majesty the emperor has granted her the entire salary of her husband, and Baron van Swieten has taken her son into his care.
A report in the Mercure universel of 30 Dec 1791 not only mentions Baron van Swieten taking Mozart’s son into his care, but also has Countess Thun adopting Mozart’s (non-existent) daughter; see the entry for 7 and 10 Dec 1791.