[SwissXC90]

I once did the math on my MY2009 D5 diesel XC90 (easy to do, it's all in VIDA)

My car, used mainly on motorways, does a regen around every 1 to 2 tanks of fuel. So that's every 600 to 1200 kms (roughly)

The more short drives you do, the more soot is generated as the engine is being driven cold a lot more. So the quicker you fill up the DPF.

With lots of short journeys, you should figure on a regen around every tank of fuel, and thus try and factor in a good motorway drive - like to your in-laws - per tank of fuel.

The car doesn't tell you when a regen is occurring and honestly, I have never noticed any regen action in 3 years of ownership of my MY2009 D5 diesel.

There is a safety margin built in: the car will tell you when it hasn't been able to do a regen and the DPF is getting too full. At that time, you MUST go for a motorway drive for at least 30min to allow the engine to get hot and do a regen.
If you don't, you risk a blocked DPF, requiring DPF removal and cleaning (at a cost to you).

(And yes, some people will jump in and say any diesel car with DPF is absolutely the wrong car for short city journeys... as the DPF will get blocked easily... and this will generally apply whatever the make of car)

To further prevent blocked DPFs, tell your kids to walk, bike or take the bus to school....