I am looking at second language development for children through play activities. I can see a a lot of second language use through the child's monologue with herself while playing but need to find research on the subject.
No references, but an anecdote. One day when my daughter was young, maybe 2 or 3, I walked downstairs to see her alone, jumping on the couch. Not noticing me, she was saying, "I'm doing this. I'm doing this." She did this in time with her jumping, emphasizing "this" each time she hit the couch.
I would suggest that you look at the cognitive and language development work done in the old Soviet Union and Russia. Lots of work has been done based upon the ideas of Lev Vygotsky regarding the evolution of inner speech. Another really get book that deals with intrapersonal narrative is the book "Narrative in the Crib" Edited by Katherine Nelson in 1989 out of Harvard University Press. These is a book that takes the intrapersonal narratives of a child and give s the data to a number of researchers who do their own analyses....this book is a wonderful theoretical and methodological feast!
you may have a look at some writings by prof. Carol Lidz . also you may go to the following website and simply search for your key words, It has a valuable-all-free data base.
Play is an extremely important aspect of children's development, and adult development as well. Associated with play is laughter (mainly a public phenomienon), and smililng (mainly an individual phenomenon). Here is a PowerPoint about "Play," one about "Laughter and Smiling," and one about "Humor and Education." Enjoy: