I have two kids--a girl and a boy--who have been gardening with me since we moved out of the city. They were one and two years old when we left Manhattan for the coast of Maine. Now they are teenagers and thankfully, they still love to help me with my gardening (except if something else more exciting comes along, which is usually does). Some of their favorite garden projects we did were indoors. Some of the projects start indoors and can be moved outside into a container or into a garden.
Most of these projects have been kid tested and have passed the criteria for fun and most importantly, have been labeled by as, 'not boring.'
For some general info and advice for gardening with kids: Dirty Hands, Happy Kids
Growing celery from the bottom of a bunch, is one of the easiest and most satisfying projects I have done with kids. To start, all you need is to buy a bunch of celery and then stick the bottom of it in water. In a matter of a day or two you should see growth. But that's just the start, once it roots, you can plant the celery bottom in a container or in your garden and grow celery or celery leaves, which are great for cooking.
Another of my all time favorite kid-friendly projects is growing garlic greens indoors. One of the best things about this is that having garlic greens to cook with in the winter is a luxurious treat for parents. This project does take a little patience as it takes awhile for the garlic to grow. Fortunately it is worth the wait and once the shoots emerge they grow quickly.
Historically, people grew sweet potato vines as houseplants. I can't figure out why you hardly ever (ok, never) see them any more. It may be because sweet potato vines have been selectively bred to be ornamental, with wide variety in leaf shape, plant habit and color--some of which are spectacular. But by simply sprouting a sweet potato by submerging half of it in water, can produce a really cool plant.
A huge bonus, is that you can eat the young leaves and stems and they are really tasty.
You can also take the sprouts, also called slips, and plant them outside in your garden or in a container. They need lots of sun and take about 100-140 days to produce sweet potatoes.
This project is a little tricky for very young kids and they will need some help with it. You simply take an eggshell, poke a hole in the bottom with a needle. Then put something porous over the hole. A piece of plastic window screening, paper towel or a coffee filter, that is just big enough to cover the hole all will work.
You can paint or draw faces on your eggshells if you want to go the chia people root. You can also just decorate the eggs too.
You then fill the eggshell with potting soil, about three-quarters full, and plant oat or wheat grass seeds, covering them with more potting soil. You have to keep the soil moist and the easiest way to do this is with a spray bottle of water. The seeds sprout pretty quickly.
You can also make egg gardens by planting tiny plants, violas or small ferns look beautiful.
I have a thing about mason jars. I just love them. I use them for drinking glasses and food storage so I have tons in my kitchen. I also like making them into terrariums. There are two ways to do this. The first couldn't be easier because, you simply get a tiny plant, leave it in its tiny pot, rest it on the lid of the mason jar and then invert the glass over it and screw it shut.
The second way I like to do it is to take a tiny plant out of its little pot and plant it in the lid of the jar. You'll need a little moss for this, to make it look finished.
Any number of things can be grown in a juice box garden. You can buy small plants, or grow something from seed. I love planting pansies or violas in them that I buy in six packs in the spring. They don't usually live all that long, because the container is so small, but if you are vigilant, they can last a few weeks.
It's also fun to grow grass in juice boxes because it grows so quickly and is so easy to do. You can even garden seeds in juice boxes, when your plants are ready for transplanting, you just cut the juice box off.
You can even make your juice box into a self-watering planter by threading cotton string through the drainage holes that you've cut into the bottom. You want the strings to hang into a dish of water, while keeping the juice box above it. This is a little challenging, but you can use stones or small dishes that the juice box sits on.