the public prosecutor and the police have determined the cause of the accident was
Only the German AAIB (the BfU) can determine the cause, and investigations are ongoing. Hopelessly understaffed as they are, the final report will probably appear in 1-2 years. The public prosecutor and the police only stated that the case is closed as far as they are concerned, there being no indication of a criminal background.
Eight people in an aircraft with six seats and ran out of fuel. It beggars belief.
It's actually legal in Germany to let two children under 10 years share a seat and a belt, and to carry children under 2 years on the lap of an adult. Whether this is actually safe and sensible (no one would do this in a car) is another matter, and when coupled with running out fuel, then yes, it really beggars belief. The three surviving children lost their mother and grandmother in the accident.