Luffy is in slight shock after seeing someone physically hurt in season 1 episode 6. Other moments within the show, different characters experience moments of anxiety, but no anxiety attacks I believe (season 1)
Throughout the season there is a "fishman" character who looks like a sawshark, with the iconic nose and a fin on his back. His skin also resembles a shark's, but otherwise he is humanoid.
While it does not show the head being squashed, Alvida does rear up her mace during an interrogation and with her body and the swinging motion being the thing the camera focuses on, the sound of something being struck is heard, followed by a quick pool of blood that a cabin boy has to clean soon after. Roughly 7 mins into the episode.
A character's teeth are damaged and they all suddenly fall out, blood everywhere. A new set of teeth instantly pushes back through the gums. This is all an extreme close up
I'd argue no. One child chooses to indenture themself for their own reasons. There are also kids held captive with their parents earlier in the show. Aside form these two vague instances, I don't think there's anything else in season one
Unfortunately, the whole setting is based on a giant ocean world with islands being the only source of land that people live on. Sea travel in boats and unnatural flotation devices (such as barrels) and shots of ocean happen on a constant basis.
(Season 1) Koby often listens to Garp’s private conversations without him knowing. Garp later finds out and quickly dissaproves of this, and Koby does it again afterwards.