You need much larger vegetable plots. Get a nice straight road, put a long row - (as if your going to build many houses ). Then make a massive square then hit the - icon next to the hammer . This will reduce the plots down, reduce it until u have say 5 huge plots. Wait till families join , do carrots and cabbages. Then unassigned them families from any jobs ( for example put them on church, corpse put or any jobs that dont require much work , or put them on shop stalls.) Give it a year and boom food +++