According to Kraft, 74% of mothers swear at their kids.
https://www.marketingdive.com/news/kraft-encourages-moms-to-swear-like-a-mother-in-viral-campaign/442166/
There are people who doubt the validity of Kraft's reaearch, but I believe those doubters fall into three categories:
1. They aren't parents themselves and have no idea what it's like.
2. They are parents but their kids are exceptionally well-behaved (lucky them).
3. They are parents with supernaturally high levels of composure (Miss Frizzle and Morticia Addams fall into that category).
Parents say bad words to their kids because:
1. Their kids disappoint them.
2. Their kids disrespect them.
3. Their kids push their buttons.
4. Their kids drive them insane.