I too have 8 children, although they are all grown, and most have given me the happiness of grandchildren. To date, and for the last 35+ years, when there is a limit to a campsite, I have told the office that they are all mine...really, and we have not had a problem. Yes, I pay for every warm body. On occasion, when we are staying for a destination, like Campland on the Bay in San Diego, and I wanted to set up a campsite for a week, I would reserve two sites adjacent and set up tents, barBq, tables and chairs, and stretch out. I've never had anyone say my family was too big for the campsite.
Hope things haven't changed over the years.
Happy Trails.