The thing is hosting that many people is actually really expensive.
I just had one for forty people, ok, more folks, but I've done 25 before, and you've to think through everything from booze, to soft drinks, to food, to nibbles, to even things like crockery, cutlery, napkins and glasses, I bought all disposable ones in case of mishaps. Even if you only did burgers, that's probably 35 burgers, as you need to account for one to two each depending on age. Can you cook 35 burgers easily? It really needs to be thought through. You can do big pots of curry or lasagne, but need to account for the kids and what they will eat. Baked potatoes is a good one.
There isn't going to be enough room in the house to serve food and drink comfortably with twelve kids running round and you can't chuck em outside if it rains or when they need feeding.
So that means you have no choice but to use outside, and when you use outside, then you need to think through the weather implications. You also need to think through seating. Folks don't want to be standing for three hours depending on age, and especially if they have to feed children. Also you need to think about parking. Can they all get parked?
I'm not trying to be negative, but the reality is this is a big undertaking.
I'd possibly look at hiring a community centre or town hall if funds are tight, they usually have all the table and seating stuff you need, and you can bring in your own food and disposable crockery, tumblers and cutlery.