Robyn,
Offering children a playful opportunity to explore magnets is very much in keeping with the inquiry process as described by the Framework for Inquiry and perfectly fits the SESE Science Curriculum for Infants (• investigate the fact that magnets attract certain materials /• investigate materials for different properties, for example materials that are attracted by magnets )
Through their play they will explore and wonder. If they then form the mental model that metals are magnetic it is valuable to include some metals that are not magnetic in the materials that the children test. Coins are an easy option, as are jewelry items made from silver or gold, and aluminium cans.
The curriculum for 1st and 2nd class looks at specific metals: (• investigate that magnets attract magnetic materials, such as iron and steel). So, depending on the school plan for Science, you may want to plan for play with Infants and a deeper exploration at 1st/2nd class level.