Keep in mind they all do a swimming motion when you pick them up especially if you don't put a hand under them. They don't feel secure when you pick them up so they all kick those legs around.. even a 60 pount land tortoise will do that when you lift it up off the ground.

It may be a baby box turtle but it could also be a baby mud or musk turtle. Do a web search for mud and musk turtle, you'll find a lot of photos of them.
-----
PHRatz