If the point of the inner-child movement is to cure adult problems, it doesn't work. Reliving childhood traumas gives you a nice afterglow, but it lasts only for hours or days. There is no evidence it changes adult problems.
Optimistic people generally feel that good things will last a long time and will have a beneficial effect on everything they do. And they think that bad things are isolated: They won't last too long and won't affect other parts of life.