You can do the fierce teacher act and order everyone to take a book to read in silence, but that can make some classes try to rebel against you. Usually it's less stressful if you engage the class in an activity that they are interested in.
With that in mind, here's an idea for relieving a Primary 1 or Primary 2 class. It's not necessarily educational, but since you're just relieving the class, it doesn't hurt to do something fun at the same time! And the materials needed are easily found in school, or in your students' schoolbags.
Hand Animals
Materials needed: Paper, pencil, colouring materials
Time: One period ( Inclusive of you giving the class instructions on how to carry this out )
What to do:
1. Put hand on paper.
2. Draw outline of hand.
3. Add eyes, hooves, hair to make it look like an animal.
4. Colour.
Easy isn't it? This can be easily done by most Primary 1 or Primary 2 students. If you want to make it more interesting, you can draw a weird-looking animal, or make it into an alien instead. Demonstrate it first, so that they can see how to do it, and then let them loose to their imaginations!