Spell StopAtTwo like this when referring to the collection of concepts. Use StopAtTwo.org to refer to the website or organization. When stating that we must stop at two children, then it should be written as a normal sentence.
Refer to the TwoFourEight and OneTwoFour algorithm like this.
If you want to refer to the website, StopAtTwo.org will work, but better is StopAtTwo. Better yet, is to provide the logo and text like this:
We support StopAtTwo