It's too late to start tomato seeds. By the time the seedlings are ready to place in the ground, temperatures may be high enough to threaten the development of blooms and pollination. Buy tomato plants from the nursery, this year. Next year, start the seed in January. If you don't have room for a large tomato plant, try the patio varieties that do very well in pots.
I gardened with my students for several years before our community garden was taken from us. I found that children love anything they can pop in their mouths right there in the garden — cherry tomatoes, beans (purple or yellow are easier to find), peas, broccoli, ... A faucet nearby is handy for rinsing the veggies before the kids pop them in their mouths.
