I'm starting to reconnect with some of my old friends from high school but they have a 5-year-old now and I want to make a good impression but I don't really know how to interact with children. Do I just like ask them what their favorite Disney movie is or something?
Likely most 5 y/os once they realize you're friends with their parents will want to jabber at you themselves. Just talk to them about what they make it obvious they want to talk about at first. And don't talk in a baby voice, IE raise your voice up high and stuff-- They're little humans by that age.
Also, play dumb. Let them tell you things you already know. And when they tell you something wrong, guide them to the right answer instead of making them feel bad for being confidently wrong.