Yeah I mean I get that, but with his knowledge and connection with the prince, I figured he would've known that the owners are connected to the merchant guild therefore having the capabilities to teach a child simple arithmetic, also given that they run an inn so the kid could've learned it just by that. It was unnecessary suspicion of a kid. Her intelligence contrary to her status could be also interpreted as being smarter than others, and that doesn't have to give them a need to have a watchful eye from a literal royalty. Sorry for the rant, but this is solely my opinion lmao. I just feel that even if you're a commoner, you could also be smart, as established from a number of mangas/novels that have commoners as smart protagonists.
The way Will became suspicious of a CHILD??? Just BC she was smart for her age and status? Like??????? AND TO INCLUDE IT ON A REPORT FOR THE PRINCE?????? WHAT????? Guys, you don't need to go that far to create a reason for establishing relations with royalty or nobility. You can do that with the magic outburst alone ಠ益ಠ