How do you think teachers manage with 30!
teachers do NOT manage 30 kids at meal time, during movie nights, when they go on outings.. they ask for parents helper and they have specific ratios depending on the set up of the place they are visiting. Around here when the kids walk across town for a visit, or take the train, it's at least 1 adult for 3 children or the day out doesn't happen.
When you host a party in a soft play, a farm, or a sport center, the party prices include 1 adult entry anyway, and they can purchase their own refreshments or the party hosts provide some drinks and nibbles - each family decide.
It's so entitled and rude to expect the host to look after all the kids, help them with toilets, ensure they don't get hurt or run away, serve the food and so on.
Soft play etc are great for that, you can bring another sibling and pay separately, so you don't impose on the host who won't even know if another child is around - unless they have reserved the entire soft play.
Thankfully, most people in my area seem to have manners.