Caught in the Act of Snooping

I know I shouldn't have done it, but last night when my kids were out with their friends, I just couldn't resist. I went into their room to grab a forgotten water bottle and ended up skimming through some text messages on my son's phone. He's been acting strange lately, like he has this big secret or something. There was one message from his friend that made me feel really bad - they were discussing how to prank someone at school the next day! I should have just taken back what I saw and not let it bother me, but now every time I see my son, all I can think about is who he might be planning pranks on. Maybe I'll tell him that I checked his phone and we can talk about why it's wrong to do those kinds of things, but part of me wants to pretend nothing happened...