As with most cartoons, there are some mild sex jokes and innuendos that will go over most kid's heads.

As a show centered on teenage characters, there is some romantic aspects to the series such as: crushs, love triangles, flirting, dating, boyfriends/girlfriends etc. There is never any nudity or sex.

Various female characters wear clothing that is low cut or exposes the midriff.

There's never any red or human blood. But there is some monster and ghost blood, which is always green.

Since Danny Phantom is a superhero show, there is tons of stylized fantasy violence including: punching, kicking, bullying, superpowers (such as shooting lasers from hands), use of various kinds of sci-fi weapons etc.

Sometimes characters threaten to kill or injure one another.

No swearing, but there is some mild name calling such as: stupid, idiot, moron, shut up etc.

None.

In the episode, "Prisoners of Love," there are three men spitting tobacco in a spittoon. In fact, the town they live in is called "spittoon."

Mild/Moderate for neurodivergent viewers.

There is tons of action and fighting throughout the show. Some of the ghost villains have intermediating appearances and powers which may frighten young children.