Seed packets and catalogs advise planting in full sun, but they will do well in our climate with an eastern exposure that gets morning sun. Nasturtiums, Tropaeolum spp. They aren't too particular about sun exposure or soil. Seed directly into the Garden. And don't forget snapdragons, Antirrhinum majus , a flower children have loved for generations.
Snapdragons come in many colors and sizes.
Buy bedding plants at local Garden centers. Two easy and appealing perennial plants might fit your space and tickle your child's fancy. Lamb's ear, Stachys byzantina , with its fuzzy succulent leaves and silvery green color, is a nice edging plant for a flower Garden or path. Children love touching and stroking it because it really does feel like a lamb's ear. It will come back next year, a source of pride and enjoyment for the young Gardener.