My suggestion would be to look at the existing literature.
Blake, Rand, Tingley, and Warneken (2015) "introduce a novel implementation of the repeated Prisoner's Dilemma (PD) designed for children to examine whether repeated interactions can successfully promote cooperation in 10 and 11 year olds."
Dealing with younger children (ages 6-11), Fan (2000) reports on a study of "children’s behavior in a prisoner’s dilemma game."
A classic treatment is Tedeschi, Hiester, and Gahagan (1969), which modified the Prisoner's Dilemma Game for a study of children ages 8 to 10.
Multiple papers have been written on how children with autism do or do not cooperate in the Prisoner's Dilemma, if that's a concern.
A journal search for
"prisoner's dilemma" children "game theory" came back with about 1000 references. You could limit that to recent studies, or include additional search terms such as "teenager" if you wish. Pick a few studies and read the methodology section for ideas.
Blake, P. R., Rand, D. G., Tingley, D., & Warneken, F. (2015). The shadow of the future promotes cooperation in a repeated prisoner's dilemma for children. Scientific Reports (Nature Publisher Group), 5, 14559. doi:10.1038/srep14559
Fan, C.-P. (2000). Teaching children cooperation — An application of experimental game theory. Journal of Economic Behavior & Organization, 41(3), 191–209. doi:10.1016/s0167-2681(99)00072-4
Tedeschi, J. T., Hiester, D., & Gahagan, J. P. (1969). Matrix values and the behavior of children in the Prisoners Dilemma Game. Child Development, 40(2), 517. doi:10.2307/1127419