> I think what you say to kids, and what you say to adults should be different.

I strongly disagree. Do you have children? Kids are smart and surprisingly logical. You don't need to molly coddle them about the value of hard work or even that they have different abilities to each other. You can deliver the news that they aren't as strong as their sister in a nice way just like you can deliver the news that an employee isn't as productive as their coworker in a nice way (and obviously avoid delivering it at all if possible in both cases).

If you want good parenting advice just watch Bluey. Look at how they talk to their children.