Veronica,
a nice set of materials for this activity are the set from the module, these are used in a few of the ESERO activities.
The floating and sinking from ESERO appears as “Does Saturn Float?” This includes an attractive poster for children to use to record their predictions.
Which characteristics would you expect children to identify as making a difference to floating and sinking? Please note that density is not used in primary science, rather objects can be described as heavy for their size. Would you have materials that can be shaped, such as tin foil? In this case you can find that it both sinks and floats, depending on shape that could lead to an interesting “take the next step.”