The current system of Dmv refund for large families encourages large families to buy Euro 5 engines, as the tax refund is significantly higher for second-hand vehicles.
 
As an example, buying a 2015 Sharan with an EU5 engine, where the tax refund is around €1400, but only around €300 for the same year of the car with an EU6 engine.
Given the current situation, it is more advantageous to buy an EU5 engine, which is the nonsense of the incentive given to large families, as it encourages the purchase of a vehicle of a lower environmental standard.