Some very, very brief references.

The term 'sex' is mentioned twice in the entire series in a sexual content.

Sometimes there is really brief comic violence.

Sometimes there is some mild violence in the ghost town and/or Hawaii episodes.

The episode "Bobby's Hero" has some very unrealistic but disturbing violence.

Just some name calling.

There is an episode where one of the main characters tries smoking to fit in, however hates it.

I wouldn't say frightening but one episode shows a family adopting and deals with the topic of racism. This can be a difficult topic or younger children to understand

The ghost town episodes and the Hawaii episodes may be scary and/or intense.