Thanks for tips, Roland. I was able to put the rubber to a shape close enough so children could understand those pictures at my weekend workshop 
Later, I want to learn more with this because it is not intuitive so "just click" method does not work - even for me who worked with computer graphics for years and used Bezier shapes a lot...
Later, I want to learn more with this because it is not intuitive so "just click" method does not work - even for me who worked with computer graphics for years and used Bezier shapes a lot...