If you mean teddy sized to some humans (like a foot tall or thereabouts), for both Bobby Loran and Chase Lisong, I think the first reaction would be something like “What the fuck, dude.”

Chase would tease, but he’d be more likely to notice that Jacob is freaked out and try to also focus on getting him back to normal. Y’know, still messing with him here and there but also recognizing that it’s kinda scary.

Bobby would probably tease him a lot more. Pushing the little guy around in his fascination over the change. None of them are really used to Jacob not being the biggest and strongest of the group. Bobby might get a little carried away, but Chase would step in to tell him off before long.

If you mean extra smol Jacob (teddy sized to little guys like Sam), Jacob would have to really hope no one’s first reaction is to grab. It’s way too easy to accidentally hurt him at that size.