When planning a vegetable garden there are a number of factors to keep in mind. Absolutely the most important is the quality of your soil. Whether you purchase soil for filling raised beds or you plan to use the native soil in your yard, it needs to contain a large amount of compost. The most effective, sustainable, and I would say, the most satisfying way, to enrich your soil is by making your own compost.
There are 4 basic ingredients to making compost: air, water, carbon and nitrogen. You don't need to be a scientist to get this right! An easier way to think of it is to mix, in fairly equal amounts, brown ingredients and green. Brown ingredients would be dried leaves, straw, wood chips, or even shredded paper. If your kids have birds, mice or gerbils, their old bedding is perfect for this. Green ingredients can be grass clippings (with no chemicals!), vegetable and fruit trimmings, coffee grounds (excellent for gardens, and your local coffee shop may be willing to bag those for you), and manure (not from dogs or cats, again, from those pets like birds or rabbits would be fine, mine comes from our chicken coop). You want to aerate it all periodically by raking or with a pitchfork and keep it moist but not sopping wet. The compost is ready when it is all dark brown, crumbly, and looks like soil. You should count on the process taking a few months, and then add it liberally to your garden, even 80% compost to soil rate is good (great, actually).