YABU, it's their wedding and they want to have the most important people to them there. Depending on ages etc, you can often find that between your friends, there are A LOT of children.
Most wedding venues seat and charge up to c. 120 people, the only discount kids get is on food. This can mean you pay up to £5-800 for a family of four.
We had children of family / wedding party and babies too young to leave parents but no others. If we HAD invited everyone else's, there would have been another THIRTY children! That's 15 LESS couples we could have asked.
This then means bride and groom have to choose between THEIR friends, and other people's children. This wasn't a difficult choice for us!
Lastly, your point re family children, don't forget that family means aunts, uncles etc too, all of whom will be the grandparents of many of the family DC. So by not inviting family DC but inviting their most trusted babysitters in many cases, you can put family in a v difficult position and often mean they are unable to come because they don't want to leave kids (often overnight... Not everyone had family on their doorstep) with unfamiliar people.
Finally, if I was your friend and knew that you'd described the biggest day of my life as a "fucking wedding" I'd be gutted. Shame on you.