Rarity is not something you think of when it comes to Piet Zwart's designs. His modular kitchens have been in production for like 75 years. He designed both the post office AND the telephone company in the Netherlands. And basically, if it hadn't been for WWII, there'd be 10x as many of these beechwood and aluminum kids' chairs in existence as there are today.
Zwart designed the chair as a kit, but only ever ended up producing them for a Montessori school in Wassenaar, a suburb of The Hague, in 1937. But the 40 chairs were obliterated--along with the school, of course--in the war, and only the four that Zwart kept for his own kids survived.
This one, one of two left in private hands, sold last week at Christie's Amsterdam for a healthy €21,250--whoops, to the Museum Boijmans Van Beuningen in Rotterdam.
Lot 663: A DUTCH BEECHWOOD AND ALUMINIUM CHILD'S CHAIR designed by Piet Zwart [christies.com]
My grandmother had a seat like this, it was actually a high chair that had a built in potty. When my grandfather passed, she put it at the curb. I so wonder if it would have been worth anything!