Start with planting in used empty Jars left in the storeroom.

Fill the Jar with soil and plant a small plant selected by your kid. It would be more fun to color the jar with his favorite color.

After planting irrigate the plants as per need and keep in direct sunlight for the day.

While in the planting process involve your child fully, if possible ask him to help with the planting.

Once your kid gets aware, prepare an action plan and make as many plants in different jars.

Also teach your kid to monitor the growth and how to maintain the plants with daily watering and fertilization.

Give your kid the responsibility of seeing each and every plant so that if plants are not in sufficient grow then he can shift it to direct sunlight.

Show your kid about use of fertilizer and basic knowledge of pesticides (keep your kids away from pesticides)
In the same way, introduce carrot by planting carrot tops. Cut off the top of a carrot.
Make sure that the carrot is green inside, for it to grow.

Put the cut top in a bowl of water so that the water covers the base, allowing the top to stay above the surface. You'll start to see new growth within a week.

Gardening projects for kids is one the most fun activities to have with your kid. Potato for example is easy to grow.

Use old potato that has begun to sprout, remove a few inches of the sprouted end.

Use toothpicks or sharp stick to support the potato over a glass (a color jar) filled with water.

Place the cut side down in the water, and take the jar to a sunny sport. In a few week or so the potatoes vine will grow out. Let your kid keep water level above the cut end of the potato