The box might not be big enough to fit a whole person, but it's big enough for someone to put their hand inside, so it doesn't mean "touch" (although there probably is some touching, but inside).
As for your sentences, "in my body", "in the ball" and "in my... dolls" all mean to be inside.
The first one sounds sexual.
The second one is odd, because you can't really be in a ball, except for maybe when you put your fingers in a bowling ball.
The third one is OK if you can go inside the dolls (for example, a matryoshka doll)
Also, some of the sentences aren't natural, but I'm just concentrating on the "in" part.