We are trying to decide which size flooring would be best for our kitchen. We have picked out the 18x18 squares of vinyl tiles but now my husband said because our kitchen is only a 12'x12' the bigger ones would make it look smaller. I need help, I'm not sure if we need the 18x18 or 12x12 inches tiles.

Either size will work in a 12' x 12' room. Large tile size is only a problem in a small room like a bathroom, where it's easy to notice that the room is only a couple of tiles wide or long.

One tip if you want the room to look larger: Install the pattern at a 45 degree angle to the direction of the room. The eye tends to follow the line of the tile edge, running them at a diagonal makes for a long line.

You don't say if these vinyl tiles have a distinct pattern or if they have a 'grout line'. If they do then this will help if you run them on a diagonal. however, if the tile color and pattern is neutral so that once installed it looks more like one solid floor, then it doesn't matter what size or direction you run them in.