Hi Joël,

I think you have to make a clear distinction between visual data and non-verbal data because they are not necessarily the same thing. From my perspective when someone talks about non-verbal I think body language and facial expressions and for drawings and collages I would talk about visual response or graphic elicitation. 

For a more developmental approach I would suggest CHILDREN'S DRAWINGS: The Genesis and Nature of Graphic Representation. A Developmental Study, by Antonio Machón, Fibulas Publishers, 2013. https://www.academia.edu/5412148/CHILDRENS_DRAWINGS._The_Genesis_and_Nature_of_Graphic_Representation._A_Developmental._Foreword_Elliot_W_Eisner_Study_by_Antonio_Machon

For a more socio-cultural approach I suggest Visual Methodologies: An Introduction to Researching with Visual Materials, by Gillian Rose - Open University, UK https://uk.sagepub.com/en-gb/eur/visual-methodologies/book235926 

Hope this helps!

Tank you very much Aline :-)

Thank you very much dear Chalamalla

best regards

Joël