These tubs were used for doing laundry, everybody had them and if it were hot outside, the kids used them to fill them up with water and play around in them.
Additional 2011/02/27: These photos were taken with a Philips Box Flash camera on 620 format film, see here. My father used to have one of these; he worked at Philips almost all his life so no doubt he could buy it at a discount from the company store. The story is that he lent it to a neighbour who accidentally dropped it in a river in Germany. The camera was recovered from the river somewhere downstream and via the police report made it back to my father 6 months later, and it still worked.