Work at their height
You don’t like a work surface that’s too high, low or wobbly, and neither do kids. You can buy child-size workbenches from school supply catalogs, but they’re expensive. You can also cut down an existing workbench, or you can easily make one yourself.
The workbench top should be at least 2 x 4 ft. and stand 24 in. high for preschoolers and 27 in. high for elementary-age kids. An easy way to stabilize it is to add a lower shelf and pile on some bricks.
Image courtesy of builtbykids.com