How can I make sure I treat my kids fairly if one seems naturally smarter than the other?

Hi parents,
I have two kids—one seems to pick things up quickly, the other struggles more with school and learning new skills. I try to encourage both, but I sometimes worry that I might unintentionally favor the “smarter” one.

How do you make sure you treat your kids fairly and give each of them the support they need, without letting differences in ability affect your attention or expectations?