For my son's 1st birthday, I ordered custom M&M's that had his name & birthdate on one color and 1st birthday on the other color. I made treat bags for everyone with the M&M's and other things.
If you are looking to entertain the kids, you could go to Michael's and get some of those foam craft pieces. You can get a container for around $7 and it would be enough to keep all the kids busy. These are foam pieces in a theme (Halloween, THanksgiving, etc.) that have a label that peels off them on the back and you can stick them to something, like a foam sticker. The kids could have a piece of cardboard and cut that in the shape of a frame and each kid gets to decorate the frame with the foam stickers. There is no mess because they are not using any other supplies. My son and I do this during the holiday time with the Christmas foam pieces and make everyones gift tags with these foam stickers.
I agree that whenever I take my kids somewhere, even to a restaurant, I always pack things to keep them busy. However, I think if you are having a gathering at your house then you should be somewhat responsible for keeping them entertained and not expect the parents to bring things to keep their own kids busy at your house. You don't have to spend a lot or even anything on activites but you should come up with things the kids can do. You could create a scavenger hunt around the dining area and the kids have to find all the items.
I'm sure whatever you do it will be great.