Take a peek at this video from YouTube to see one example of how it can be done. Things that stand out about it:

• A variety of materials from the start: different sizes of cardboard, different materials to incorporate
• Flexibility! Dot paints weren't in the original materials she set out, but she added them in when the younger child joined in because they are easier for her to use
• Open-ended: there is no right or wrong way for this to be done, meaning it's naturally more accessible for kids of all ages