we use them at the nursery where I work
the children use them in the sand tray, in the water tray and for storing things like collage bits and pieces and scissors in the workshop area.
They are ideal because they are small and can be replaced when they get trashed
We also use the ones with the carry handle, that have 6 little pots in, for storing things like magnetic letters and other small things
Also, we use them when planting seeds, like sunflowers etc.
So, yes they can be re-used.