As your tomatoes begin to grow you will likely notice little shoots that begin to branch off from the stem. These little shoots are called "suckers" because they take the energy from the rest of the plant and can cause the plant to bear fewer fruits. Simply pinch them off and discard when you can. They won't hurt your tomatoes. You'll simply find that your tomato plants bear a lot more fruit if you remove them.

If the shoot has grown for a while and is now thicker than a pencil, just let it go as removing it could harm the plant. 

Tops and Bottoms is a great activity to help children better understand how garden vegetables grow and what part of the vegetable they can eat.  This lesson can be as simple as drawing pictures on a board as shown below. A supplemental image could be included showing a radish that grows "from the bottom" and is ready to harvest.