Yesterday we were at a wedding of BIL and his partner. DS (2 yrs) and DD (1yr) were page boy and bridesmaid - not the only ones. DH and DSIL were witnesses.
It was in France so first civil ceremony, then church. The civil was important, not just bureaucracy.
So, DH and kids, DSIL and her husband who was taking photos for the ceremony and DMIL and DFIL and I all arrive together. We're running late. It starts raining and we've got to walk about 500 metres to get to the ceremony. Everybody had umbrellas, apart from DH and I (didn't have any with us as when we packed to leave, it was supposed to be sunny). Everyone was standing outside, with umbrellas or under the lid of the boot sheltering. I realised the time and that they would be really late if they didn't leave then, so said I'd wait with DD (no rain cover for buggy) until it stopped raining then come up. DH hesitated, the rest turned and went.
Up until here, I have no problem.
By the time they arrived at the registry office (equivalent) the rain was harder and it was clear that it wasn't about to stop any time soon.
I ended up staying in the car with DD for the whole ceremony. There was absolutely no way we could come without coats or umbrellas.
I think that it would have been considerate to ask someone in the extended family to nip down with some umbrellas so we could join, when it was clear that the rain wasn't going to stop. They'd have missed 10 mins max of the ceremony if they'd come when DH etc arrived. They did ask someone in extended family (DH couldn't leave after the ceremony apparently) to come after the ceremony had finished.
So WIBU to be a bit upset at being left in the car? DH says I volunteered, so how did they know I didn't want to be in the car 
and I think that having driven 10 hours to get here with two young children, it was obvious that sitting in the car alone with DD wasn't my plan.