My first thought was Sunflowers. The seeds are large enough for little hands and have a fast germination rate, so children see results quickly ... and who doesn't love sunflowers! Marigolds always seem to be a favorite flower with children too. For a "Salad Garden" lettuce and cherry tomato's are a great choice. With tomato's you could either start them from seed or purchase a small seedling plant.
I agree with whoever mentioned watering ... when my nieces were young they loved watering all of my plants, either with the garden hose (which ended up with them getting soaked as well
or a watering can. A number of years ago either Target or Walmart gardening center carryied children's gardening gloves, boots, and tools ... all miniature in size for little hands and it does make them feel all grown up to have their own gardening items. One of my nieces used to put my gloves on and she loved playing in the beds and planting stuff even using big girl tools.
If it hasn't been done already someone who's good at writing should write an article for ATP about "Gardening with Children".
