I don't believe one needs to engage in childish activitys in therapy as such. Regression isn't about playing with toys, its about processing very young feelings. Ie that moment when a childs arms spring out when it feels being dropped, those are feelings I still have that were never processed or contained. That's what regression is about. Uding art as a form of expression is another issue. I regress to very early emotions but have no desire to start playing games as a child, its not the same thing.