aricad 02/12/2015 at 02:31pm
Try a collaborative piece like the ones shown here

https://www.pinterest.com/greensarahjean/art-lessons-collaborative/

Honestly it depend on the medium and age of the kid, too large of a canvas can be overwhelming and daunting. Sometimes small will lead to more detailed work, less rushing.

paintpeace 04/03/2015 at 10:35pm
I think Bigger just has pizazz. Unfortunately, it takes self discipline to finish a big piece (challenging for kids), and storage while its drying? Impossible if you have more than one class a day.