... is your trust.
Trust that they're making the right decisions.
Trust that, in case they make a mistake, they would do better next time.
Trust that they can figure things out.
Trust that they can make their dreams a reality.
Trust that they can become whom God created them to be (not whom we want them to be).
Because they can become true to themselves only when we give them our trust.
They can grow only when they know that we trust them enough to learn from their mistakes.
They can realize their potential only when we give them room to operate. And that requires a lot of trust.
Besides, doesn't it feel more encouraging and motivating when you know someone believes in you and roots for you to succeed?
P.S. The best thing you can give is more obvious: love. (And we don't talk about the obvious often. Still, let's not take the obvious for granted.)