I agree not to get stressed but I would suggest that it is worth talking through good revision practice - as good practice rather than actual results this time.
Bright children can probably wing it through school exams for the first few years but that doesn't set good foundations for when they need to set to work.
Many can do 'well enough' without working so they don't necessarily learn any lessons from lack of revision in year 7!
Also agree that huge amounts shouldn't be needed but what they do could be done in a focussed way - ie not just sitting in front of a text book for a couple of hours
Maybe choose say two subjects where revision might be helpful - either DC struggles a bit or the type of subject where they need to learn facts - and come up with a strategy together for those?
And don't worry too much about setting - usually there is fluidity between sets at this stage.