In "Adventures in Supersitting" when Cherry accidently found out, she had just met Phoebe and didn't know her very well and so she was much more quick to make a decision as to how to react to it. Cherry, as an airheaded; impulsive teenage girl, also makes snap decisions without thinking about them, so revealing the truth about the Thundermans wasn't because she didn't know them personally, but just because she is wired to respond quickly without considering the consequences of her actions. By the time "A Hero is Born" came around, Cherry has gotten to know Phoebe personally and they think of each other as their best friend. Thus, Cherry knows her well enough to know that it has to be kept a secret and is not only much quicker in figuring it out, but thinking it over as well as she can now understand the value of the secret itself.

In "Restaurant Crashers, " it seems like it is more for recently learned secrets rather than long-term secrets. Plus, Phoebe, over a long period of time has been reminded of and learned the value and importance of not telling anyone about their powers and thus, has sort of been conditioned not to impulsively reveal the truth. When she tells Cherry in "A Hero is Born," it's not done on an impulse as Phoebe seems to have thought long and hard about a point when she would confess the truth to Cherry and confide it to her.