Characters in shippings don't have to be thought of as being their current ages when the shipping happens. You can see two children of the opposite *** getting along, and then imagine them as a potential couple in the future. There is nothing wrong with that. Heck, if you think about it, just about all the fans have already been doing this for years with kids. Naruto/Hinata, Sasuke/Sakura, Shikamaru/Temari etc... They were all still kids around 12 - 14 when people started shipping them.
The problem with fans and shipping when it comes to kids is mainly that when people hear a ship, they assume two things:
1. They assume that the shipper wants the couple to happen right here right now.
2. They assume that pairing = something rated R, that shipping automatically means passionate coitus or something like that.