Anyone notice that in many cartoons you can actually understand swear words in the muttering etc.

The only cartoon I can think of is Popeye, but there are quite a few that will have a few swear words in it. But Popeye has at least one swear word in just about every toon written for him.

Between him and Brutus I am sure Sweet Pee will turn out pretty raunchy.
In the 443.5 hours of children's programming analyzed by the PTC,
they found

858 incidents of verbal aggression (e.g. abusive yelling, mean-spirited insults and put-downs)

250 incidents of offensive language (such as excretory references or euphemisms for obscene language)

595 incidents of disruptive, disrespectful or otherwise problematic attitudes and behaviors

275 incidents of sexual content

so please don't tell me there are none.
http://www.parentstv.org/PTC/publications/reports/childrensstudy/main.asp

this link is just one I found explaining these details.