What does the term "kiddo" mean in this situation?

Anonymous
So there's this guy I know. We just met, and he asked me earlier in the week if I had a free night this week to show him around (he's new to the area) so we went on a hike and got icecream. It went super well, and was a lot of fun--not awkward at all, and we talked about a potential 2nd date, watching a movie together. (Which I friendly said we should watch, then later on he said so when should we watch it) anyways...last night we were texting and I said I better head to bed, but I hope ya had a great night. And he replied and said part of his response was "goodnight kiddo, text me tomorrow" what does that mean in this case?--the goodnight kiddo?
What does the term "kiddo" mean in this situation?
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