I had asked him MANY times in days leading up to it to be SURE he recalled they had this big game and party and he assured me he would have them there EARLY. I had offered to help or bring them myself if he wanted and he said he was all set.
IF you have to say it more then once, it's nagging............
Maybe he doesn't like to be told MANY times and purposely didn’t get them there.
I’m certainly NOT putting the blame on you just offering a possible view from his ill side of things.
Moving forward, anything that is that important to your kids, he should be left out of the responsibility of transporting them and you just do it yourself.
My ex was a nasty SOB and he would intentionally do things or forget on anything I would ask him to do. Childlike but sadly this was HIS mentality – all about him – never about his kids.