How can I tell you that I'm thinking of the baby sitter and her brothers little secret?
This sounds interesting. You can just tell me what the secret is.
Yes they have sex, regularly like clockwork every night at 12pm
It can be freeing to let others know about someone's secret, but it is also quite wrong. This is none of your business, disregard what they do in their personal life. Exposing secrets of others might want someone to find out about yours and do the same to you.
I though about it for a good week. I thought about blackmailing her.
Telling a secret would be wrong unless the secret involves someone being hurt or taken advantage of.