1st Baseman mitt at 2nd base?

[FomerUmpire]

Hello,

I stopped umpiring about ten years ago and did mostly HS ball back then.

Tonight, I was watching my nephew's 14u game-MLB Rules being used. The second baseman for the Wart Hogs(I am not joking...they are really called that! LOL) was wearing a 1st Baseman's mitt.

I am pretty sure that High School Baseball rules allow a player to wear a mitt anywhere. I thought that MLB Rules prohibit it. Is there an online version of the rules? Can you help an old guy out?

I think I am the only one that noticed and I doubt anyone on either team cared but, now it is one of those things bothering me and NOW, I just have to know what that stinking rule is.

Thanks!

Uncle Bill