Note: I want to try not mentioning sex/gender to see how answers may depend on this.
Consider 2 children Ashanti Smith, 17 years old, and younger sibling Bidatz Smith, 9 years old.
Ashanti has recently started to be a tutor for several of Ashanti's own classmates (actually people in the same year and school but not necessarily the same class). This includes Mikoto and 2 of Mikoto's friends (all are 17 years old), all 3 of whom recently transferred (due to academic problems, hence the tutoring) to the school of Ashanti and Bidatz. This tutorial is really paid work namely from Mikoto's parents (and the parents of the others) to the parents of Ashanti and Bidatz. The parents knew each other from before but weren't really that close, but Ashanti and Bidatz 1st met Mikoto et al just through the recent tutoring.
Early on in the tutorials, Mikoto once came over to the Smith residence for dinner where Bidatz and Mikoto had become very friendly. Later on, Mikoto, Ashanti and Bidatz hung out together and then Mikoto and Bidatz exchanged contact information. Sometime later on, Mikoto and Bidatz were hanging out on their own on weekends (eg at malls or computer shops), where by 'their own', I mean without the presence of Ashanti, Ashanti's parents or Mikoto's parents.
Question: Can it be appropriate for Mikoto and Bidatz to hang out in this way?
Edit 1: I had an idea. Maybe the parents really trust Mikoto as if Mikoto were like a babysitter or something? Seems quite normal for 17 year olds to babysit 9 year olds...Hell even 30+ year olds baby sit 9 year olds. Yeah maybe I was just overthinking it. Idk.
Edit 2: Presumably, Bidatz got permission from Bidatz' parents. It's not like Bidatz and Mikoto were sneaking around. They were hanging out in broad daylight, and it's not like Ashanti or Mikoto's friends don't know. It's just that Ashanti and Mikoto's friends aren't with them sometimes.