Use baby food jars and punch holes in the lid and add various smells to the jars. For example: cloves, mints, petals, sawdust, onions, apples, etc. See if the children can identify these smells.
A fun variation of this activity is to make duplicates of these smells and see if the children can match the smells.
You can also take a "smell walk" and discover the various smells in our environment, such as leaves, flowers, dirt, grass, fruit, water, etc.