A happy pumpkin sprout
Starting vegetables from seed is not difficult, but does require some attention. I like to do it because I can grow what I want, it gives me a closer relationship to how the plant grows, and it's much cheaper than buying starts at the nursery. The main things to know about starting seeds is to use a good potting soil, plant the seeds the depth they want, and keep the soil consistently moist.
A good potting soil is one that is moist, has some drainage elements like vermiculite or sand, and is sterile. Unless you really know what you're doing, or you feel confident mixing your own potting soil, just get some at a nursery--I tend to buy the more expensive soil just because I know the seeds will do better in it. Cheap potting soil usually doesn't moisten evenly, has large chunky pieces, is difficult to work with, and generally isn't much of a deal in my opinion.
Planting the seeds the depth they want means don't plant them too deep! Too shallow can be a problem, too. Check the packet, if you bought the seeds in a packet. Otherwise, the general rule is that seeds are planted twice the depth of their diameter--so small seeds will be planted in a shallow hole, and large seeds will need a deeper hole. There are exceptions to this rule--some small seeds I don't even bury--lettuce, dill, poppies and anything with a seed barely visible I just pat into the soil surface. Brassicas like brocolli, collards, and kale, have tiny seeds, but like to be planted at a half inch depth.
Anything with a really large seed I usually plant directly into the soil--beans, peas, corn, pumpkins. Especially the first three will outgrow their little pot in a few weeks, so starting them in pots only buys you a short amount of time. Also, there are some plants that don't like to be transplanted--it can be done, but they lose some growing time, or may not make it. Carrots, sunflowers, cilantro, and beets are some that come to mind. They do best when directly planted in the garden.
March is a good time to start seeds--if you start seedlings of plants that prefer warm weather, you can get a jump on the season. Warm season crops are a good thing to start now from seed--put them inside on a sunny windowsill. Tomatoes, corn, peppers, summer squash, pumpkins and other winter squash. Especially this year, the tomatoes, peppers, and summer squash crops were damaged in Mexico, and the grocery had a letter explaining why the price of these three crops will be more expensive in the coming months. This is the year to grow those crops yourself, and save some money.
In our climate, zone 9b, many things can be started in pots and left out overnight this time of year. Lettuce, radishes, broccoli, and others in the brassica family (kale, kohl rabi, cabbage, etc.), bulbing fennel, amaranth, quinoa. (This is what I have sprouting right now). If you have a really hot summer, don't start brussels sprouts, or sugar snap peas, or any cold season crop that has a long growing season. In South Berkeley where I live, we have a lot of fog in the summer, and last summer I barely took off my sweater, so those rules may not apply for us.
Planting vegetables from seeds is a great activity to do with kids: they will have a great appreciation when eating, but even before then, watching the plants grow is great fun. The best part is watching the seeds sprout. This is the time when the plants need the most babying--they must not be allowed to dry out, so careful checking every day, and usually daily watering is necessary. It takes time, but pays off.
As you watch seeds sprout, you'll get the know the character of each type--the fuzziness of tomatoes, the bold nature of bean sprouts, the tall skinny onions bent double at first, the tiny lettuce sprouts that even in their first leaves show the color and pattern they will take on, the heart shaped radish sprouts, the cloverlike shape of brassicas. To sprout seeds is to witness the miracle of life itself. It reminds us we are a part of this thing we call "nature"--we influence it, we are present in it, we are connected to all those who have grown plants in the past, and all those who will grow them when we are gone. So, plant your seeds. It's not just salad you will grow.