Your little sibling tells you things they’d never tell your parents. Guard that like it’s a job.

Being the one they tell is a position, not just a closeness. It exists because you are old enough to help and not the person who sets the rules, and it disappears permanently the first time something gets repeated upstairs. What they are really testing is whether information can be given to you safely. That answer gets settled early and does not get revisited often.

Hold the ordinary things completely, including the ones you find funny. If something is genuinely dangerous, tell them you are going to bring an adult in and then do it with them rather than behind them. Everything else stays with you.