@Creamandjamorjamandcream i was in a similar position over 10 years ago, when my brother got married.
When they announced the wedding date and stipulated that it would be child free, it was fine, as I didn’t even have a child then.
However, I found out I was pregnant a few weeks later, with DD due date 2 weeks before the wedding!
DH and I thought they’d make allowances for a 2 week old baby (if indeed she arrived on the due date and if I felt well enough to attend), but SIL refused! My brother and the whole family tried to change her mind, but she refused.
DD DID arrive 2 weeks before, so I had to make the decision of either not attending at all, or leaving DD with DH at my mums house, while I went to the wedding.
i decided to go (it was 4 hours away by train), having had an emergency C-section.
Upon reflection, I wish I hadn’t bothered - I was knackered, SIL and brother barely spoke to me, and at the reception, I was seated the furthest away from the top table, on a table of randoms I didn’t know (think ex work colleagues of my brother), so couldn’t even chat to family.
Then had to spend about half an hour in one of the hotel rooms, expressing breast milk.
Several years later, my brother and SIL split up (no surprise there!) and brother told me he was sorry, and that he’d nearly called the wedding off because of how she’d behaved.
Think carefully before deciding what to do.
I’d try and cancel as much as possible, if you can get a refund on flights or hotel, or try to get credit to fly somewhere else.
Even if you do go alone to the wedding, you’ll have no end of friends and relatives coming up asking where DH and the kids are.
In my case, all of the extended family were incredulous, asking where the baby was, when I explained that my tiny little 2 week newborn wasn’t allowed to come 🥺