Everyone likes a little variety, and kids especially like things that look strange. When it comes to vegetables, you might be surprised (or you might already know) how many of them come in purple: beans, carrots, cauliflower, eggplants, peppers, kohlrabi, radishes, turnips, tomatillos, asparagus and basil.
A commonly available purple bush bean variety called Royal Burgundy does better in cool soil than many green varieties. If you want pole beans, try Blauhilde. Purple beans turn green when they are cooked.
Purple Haze is a popular purple-skinned carrot that is orange on the inside. Johnny's also offers Cosmic Purple, which is yellow inside, and Purple Rain, a new very dark purple variety with white or purple cores. They generally turn orange or yellow when cooked.
Cauliflower comes in both orange and purple, and these coloured types are said to be more forgiving to growers than regular cauliflower. Violet Queen has a texture more similar to broccoli than cauliflower and turns green when it is cooked. Graffiti is a true cauliflower, and according to Stokes' catalogue, it turns "bluish purple" when it is cooked. Most large seed companies carry at least one of these varieties.
Eggplants are the quintessential purple vegetable. Make sure you have a nice, hot place in your garden for these ones.
If you are very lucky, you might be able to find a purple-podded pea. Try Desiree, a purple snow pea or Blue Pod Capucijners, which is usually used as a dry pea, but can also be used fresh.
Kohlrabi is already an unusual-looking vegetable and there are several purple-skinned varieties kids might enjoy growing. Early Purple Vienna is commonly available, or you might come across the hybrid Kolibri.
If you must have purple radishes, try Amethyst, or grow purple, white, pink and red together in the commonly available Easter Egg blend.
Even asparagus comes in a purple variety; Purple Passion is a variety offered as crowns from Johnny's. It turns green when cooked and may not be as hardy as some green varieties, but it is supposed to have a superior flavour.
Not really a vegetable, but basil comes in some impressive purple-leafed varieties. Purple Ruffles is commonly available, or you might see Red Rubin. Both will make red pesto.
Many of these vegetables lose their colour when cooked, but if you want to retain as much colour as possible when cooking, try adding a weak acid to the water, such as vinegar or lemon juice. According to the Fort Valley State University's College of Agriculture and Home Economics, this may help retain the colour of purple or red vegetables.
If you want to grow some things that are really different, join the Seed Savers Exchange and see what their members are offering. You might be surprised at what you find!