Hi Momma-
My parents did this with me and my sisters when we were just little ones. I was 5, my baby sister was literally just born, and my older sister was 8. We had a garden until I was in highschool.
The easiest things we started with were carrots, lettuce, and corn- white, yellow, and yes -popcorn. We eventually added tomatoes, berry vines, and 2 fruit trees, some strawberry plants, and something else I can't remember. I will say that it really cuts down on the grocery bill!
Okay, as far as your yard goes- dig up a section, get some black dirt from your local green waste landfill, or go to the store and get some miracle grow soil enrichment stuff. Mix it in with your dirt.
To plant, every area is different. In Bakersfield, CA, it's severely hot, like in Texas, BUT YOU have alot more humidty. We are considered dry.
My parents always planted in the spring, however, there are year round gardens- in the late summer, you plant squash and it blooms in the fall, orange trees (depending on their type) flourish in the wet winter months, and then tomatoes and what not in the spring. Just pick your 10 or 12 veggies and fruits and plant them by their season. A book can help, OR go to a nursery and ask the gardener there. They should be willing and able to help you out.
Lastly, as far as watering, you have a couple of options: sprinklers on a timer, a drip line, hand watering, or if you want to get super fancy, hydroponics. Hand watering can be soothing and medicinal -- go outside each morning with your son and the hose and water all the seeds as they grow. This will teach him maintenance and daily checking. As far as weeds go, just pull them out as they come up. I have found that the more stuff you have growing, the less weeds will come through. Also, plant some lavendar or mexican sage, some rosemary, etc. It takes up a large space, can be used for a number of things, and also looks pretty. It can be a stand alone, year round plant next to your herbs and veggies.
Good luck, and have loads of fun!
-E. M