Ooh I totally understand your situation.
You are definitely not in a position to go, whether it was planned like that or just an oversight, only they know.
I had similar when mine were young, everyone seemed to have child free weddings, parties that children could not go to, meals to restaurants very late at night. One time one of my sil organised a wedding anniversary for pil in a late bar that did food, it was to start at 8pm, children had to be off the premises by 9pm. It was a 4 hour journey for us to attend for one hour and most didn't turn up until close to 9pm!
We went to and organised all these events when we'd no children, tbh never even gave it any thought about whether children were allowed, maybe this is what has happened here?
It's difficult for you to arrange childcare for that amount of time, I personally wouldn't be happy getting a stranger abroad minding my children. When you don't have family close enough or able to take your children it does prevent you doing a lot. Many people won't understand this because they have family and friends coming out of their ears who are only too delighted to take their children for that amount of time.
Over the years while mine were growing up dh and myself made the decision that if something was child free only one of us went, he went to his side I went to my side of the family, tbh I wouldn't go alone to his side for a celebration.
It would have been nice to go but unfortunately you can't, all you can do is enjoy the time at home, get take away and treats and have fun with your kids.