I've driven this kid 10k km in 6 months in this car, he's never been sick before and I blame the recent meal combined with the awful smell of diesel-porky in front of us (revving hard up those bends).
He's in a high quality Britax seat using the three point harness / belt but intuitively bent towards the window resulting in some of it coming onto the alcantara and downhill from there... Most of it came on the seat and his shirt. The leather can take it and is easily cleaned, the "job" is cleaning the stitching itself. Didn't take more than 10 minutes given the small amount.
The stopping windows are actually nice considering. Typically when someone become sick windows are opened (= rubber trim / seal not so efficient), the try to bend out, barf goes down the window slit. That's worse
And thanks svxcess