I have great luck with rattlesnake beans, as well as provider. Almost any cherry tomatoes would probably do fine for the kids, as most are productive and easily grown. I'd recommend whatever plants they can buy near them of these, although they might like pear for the interesting shape. The nasturtium was a great idea! They are a bit peppery. My nieces (5 and 8) like borage flowers, which are blue and taste like cucumber. They grow easily, the flowers pop right off to eat by pulling on the center (no stems), and when the plants get too big, just remove them to clear space for other plants coming in.