https://www.suite101.com/content/how-to-make-a-party-hat-a123412
https://www.magicbob2000.com/hats.html
If you don't want cones then another way to do it is to cut out a 2D shape (crown, animals, numbers - whatever you want) and then to use a strip of 2" wind bendable card to fix to the back of it.... make the card strips about 18" - 2' long and then fit them around each child's head and secure with double sided tape
I'm not sure I explained that very well LOL - but what you are aiming for is kind of like a Red Indian headband, that fits across the forehead and then round the back of the head, with a piece at the front with your main shape on it
Kind of like this https://crafts.kaboose.com/blues-clues-party-hat.html
Another way is by using paper plates - like this https://www.enchantedlearning.com/crafts/hats/
We used to do loads of these at playgroup years ago and I did have a book of loads of different ones ... don't know where it went though
I'll have a look on amazon for you once I've got the dinner started