One wants it fixed. The other wants out.
It's too hard. I can't do it. I don't know how. This is stupid.
Said in the voice. You know the voice.
Most advice stops here and tells you not to rescue them. That is half right, and the missing half changes what you should actually do.
Because there are two of these, and they sound almost identical.
The first kind
The glue won't hold. The code won't run. The sleeve came out wrong.
This whining is about the problem. Something specific has failed and they are furious with it.
The second kind
Why do I have to. How much longer. When can I stop.
This whining is about the activity. Nothing has failed. They just do not want to be there.
One wants it fixed. The other wants out.
That distinction is the entire thing, and once you have heard it you cannot unhear it.
The first child is usually nearly through. The frustration is loud because they are close enough to see what it should look like and cannot get there yet. The only thing that helps is you not being involved. Leave them with it.
The second child is not having a grit problem. Pushing harder will not fix it, because whatever is missing was never effort. There is a different conversation to have there, and it is not about persistence.
What to say to the first kind
So you are not just standing there in silence:
"I don't know either. Come and tell me if you work it out."
Then do not step in for twenty minutes. Not five. Twenty.
That line does two things. It removes you as the authority, which is honest, because usually you genuinely do not know how their thing works. And "come and tell me" gives them a reason to solve it, because now there is someone waiting to hear.
And the obvious caveat
Step in for danger. Step in for real distress. Step in if it is genuinely beyond them.
Frustration is none of those.
The part that took me longest
You get far more of the first kind of whining when the thing was theirs to begin with.
That is the whole reason I build challenges around something a child already cares about rather than something I have decided would be good for them. Start there, and the complaining you get is the useful kind.