When someone has fully lost their inner child, that just sucks. Unfortunately the process starts way too early now, considering few people care about kids learning about decidedly mature subjects. But maybe that's just me.
Anyway, I can be kind of random and kid-like at times, but maintaining a bit of a childlike demeanor and sense of wonder is key to a healthy life, I think. I can, and often am, perfectly serious when the time comes, almost to a fault. But I can be a kid too, when it's appropriate.