15 passenger van. All the dc up through my 9yo are in some kind of carseat - we do super extended carseat/booster seats.
The reason this is so special to me is that in 2001 we bought an 8 passenger van and had 4 carseats (4dc age 5 and under). I ASSumed we would fill the van but 2 years and too many losses of both babies and part of my reproductive system later, no more carseats had been added.

That was the saddest time of my life and I finally began to accept that there would be no more babies, just a big van with too much space. So every time another seat is added I am reminded of that time and amazed at how my life has gone since then. I never, never, never take for granted now adding another seat to the van, another baby to the family.