Ah, this is now making me consider writing something on baby Xiao..... The thing is I have so many separate headcanons about young Xiao too- I love the idea of him as a small fledgling bird but also the idea of him as a pure elemental, nature spirit just as much! Regardless, I personally think he was on the shy side as a child- his character story suggests he was naive back then which leads me to believe he was curious, quiet, keen, and possessing a deep, gentle kindness that was unfortunately easily taken advantage of. I imagine him when he's little observing everything with rapt interest, from the slithering movements of earthworms to the beauty of winter's first snow. To Xiao, everything in the world must have felt beautiful and fascinating- nothing was beneath his attention. I imagine that despite being an introspective kid, he was much more expressive back then and smiled, laughed, and cried much more freely. He was just born with a heart too big for his body. I personally do really love characterizations that emphasize Xiao's childlike curiosity and how although it was something he somewhat lost during his time in enslavement, it's something that present Xiao is learning to let himself feel again.