You weren’t able to enjoy your childhood due to your past experiences and Tartaglia didn’t really get to either.

Now Tartaglia’s a Fatui Harbinger and your a famous traveling doctor who has accompanied Tartaglia for months now as he travels around Teyvat for his job.

You could be bit childish at times though, it was almost a way to make up for your lost childhood, he didn’t mind though, in fact he encouraged it.