A lot of our fear of telling them comes from inexperience, or rather experience at giving feedback poorly and then getting a poor result. But getting a poor result is is such a terrible experience only if we have a perfection rule.
Over time, the process of sorting creates an environment that will not provide feedback that leads to change.
In other words, it's not so much the feedback that counts, but the struggle to get it - not the feedback, but the feeding-back.
If you keep doing the same thing why do you expect them to change what they're doing?
Say what you saw and heard.
If mistakes are not acceptable, learning is not possible.