Tomato plants love the sun, so even if you plant them upside down, they'll find their way to the light. For a fun family project, give it a try and see for yourself. You can buy hanging planters from garden suppliers (such as gardeners.com) or make your own. Here's how.
Thoroughly clean out the bucket. Drill and cut a hole about 2 to 3 inches in diameter in the bottom of the bucket (a parent's job). Put some moss in the bottom of the bucket all around the hole to keep the tomato plant from falling out when you first hang the bucket.
Gently thread the upper 2 to 3 inches of the seedling through the hole, keeping the roots inside the bucket. While you hold the plant in place, have your child loosely pack dirt around the stem up to the root-ball. Then you can let go and add enough soil to cover the roots by about 2 inches.
Add a couple of cups of compost and more soil so the bucket is filled to just an inch or two below the rim.
Hang the bucket by its handle and water the plant thoroughly, until water starts running out of the hole. Water the tomato plant regularly, adding more soil and fertilizer if the level in the bucket falls. Keeping the bucket covered will help retain some moisture. As the plant grows out of the bottom of the bucket, its leaves will curl up toward the sun in search of the light until the tomato fruit appears and weighs them down.