Let your junior colleagues fail on a schedule within the margin of error on your planning, but keep a close enough eye on them so you know how to bail it out if they can’t pull it together with a little extra time/guidance.

Okay — still give good code reviews, but if you let them face-plant a little on design, etc, then they get experience. And you don’t look dumb when it turns out they were right. But you do look like a hero when they’re struggling to get across the line, and you whisk in to fix it.