What I did was this. I cut out lots of speech and thoughts bubbles, and stuck them all along the floor, beneath the artworks. People could then come along, and provide the portraits with 'thoughts' and 'feelings'. I discouraged people from looking up any information about the pictures until after they had done the writing; imagination was key. For some of the little children I acted as a scribe, and conversed with them in order to elicit their ideas.
What emerged at the end of the day was a rather surreal, frequently hilarious poem consisting entirely of lines that children came up with. Here it is. Enjoy!