Jumping Clay has put together kits containing all the bits you need to create Olly the octopus, including the shell for him to sit on, and all the instructions you need. This is air dry clay so it is no stress and super simple.  Jumping Clay usually offers in person workshops for kids. Obviously this year that has not been possible so they have created kits for you to make at home.

Jumping Clay Olly Octopus kit