I'm organising a wedding at the moment, and we've had to limit it to our siblings' kids only.
We've chosen a venue that we like, can afford, and is convenient to most of the guests and accessible to our 90-year-old Nans, one of whom very rarely goes out at all. We can fit in 120 max. Babes in arms count towards the head count, but not the food bill.
Family, including the sibs' kids, are the first 70 on the list. That's Nans, aunts, uncles, a few cousins that we're especially close to, and their partners, as well as our parents and siblings and their partners.
Best man, ushers and bridesmaids and their partners are another 10. These are the very, very close friends that we could phone at 3am in a crisis and vice versa. Then there are the family friends; about another 10.
We have to count ourselves!
There are 28 spaces left. That's 14 friends plus partners - 7 friends each. These are the "ordinary" friends, the ones we go out with from time to time, enjoy seeing, some of them have known for most of our lives.
If we'd invited even our cousins' children, there wouldn't have been space for any friends at all. We couldn't invite Friend A's children without inviting Friend B's children as well, it wouldn't be fair. We would love to have had all the family and friends' children, but we couldn't afford to have anywhere bigger, and in any case 120 people is way more than I'm happy with; any bigger and I'd spend the whole thing hiding.
Guest lists are REALLY difficult. If you don't want to go without your daughter, I'm sure the bride and groom will understand. It's an invitation, not a command.
Sorry for the essay, but we have so many of these threads I hope it will shed some light on how quickly the numbers add up.