In the spring you can probably start some veggies. Not sure about this time of year. Where are you located, and how cold does it get on your sunporch in the winter? You might try some cool-weather veggies if you'll have enough sun long enough into the fall. I believe anything that doesn't need to bloom to produce would work.
You can always plant an onion and grow scallions, but I don't know if boys will be too excited about that.
How old are they?
Maybe carrots? How about "miniature dinosaur trees" (broccoli)
(I heard kids love that term and will eat broccoli when you call it that).
All depends on how long your warm weather lasts. I hope others jump in here with better ideas.