Here's my Picasso technique:* I used a charcoal pencil (as I love the dark soft lines you get) and started off by drawing one element of the 'cello.
* Then I turned the page 90 degrees and drew another element, then turned the page another 90 degrees and so on.
* When all the 'cello elements were on the page, I then added straight lines connecting the various elements.
* Then I added some vase shapes of some wooden vases that were next to the 'cello and shaded in some of the blocks.
* I fixed the charcoal with a fixing spray to prevent the charcoal smudging and to allow me to paint over with gouache later on.
This is definitely a technique you could use with older children. Show them some works by Picasso and let them choose an object to draw, turning the page 90 degrees every so often.