It's common for kits, or even adults who haven't been mistreated to not take long to be friendly. I had my current two out a couple hours after bring them home at 3 years old. However it really comes down to personality, some chins are just more outgoing then others, but also kits haven't gone though puberty yet, their personality can change then. You could look at kits like little kids, they love everyone so long as they are treated well, but that doesn't mean when they grow up they will.
Another thing to point out, at 13 weeks the chin really shouldn't be getting out of cage playtime, or at most 5 minutes a day. They need their energy to grow, and kits don't know when to stop, like little kids and will play until they drop. Unfortunately with chins that can mean a drop in blood sugar not just energy, and that can lead to seizures and death.
I just want to add, I'm sure you know but, be extra careful with a chin around young kids. Toddlers and young kids don't have the fine motor skills of an adult and can easily hurt the chin by accident. Chins are a lot more fragile then most other rodents, and have what's call a floating rib cage, so if squeezed around the body you can puncture a lung with a rib. They also have very tiny bones, about the thickness of a toothpick. I'm not saying there is anything wrong with allowing contact, just, be careful. I don't recommend or allow my chins to be handled by anyone under about 12, they are really more an adult pet.