You might remember that Google reported on the last I/O that the app Digital Wellbeing should be anchored with Family Link and that parents would get even better possibilities to have some control over the Google accounts of their children under Android Q.
As Android policy reports, this seems to work right now with the current Android Q beta, if you have installed beta version 1.0.257813777.beta of the Digital Wellbeing app in parallel. Then you won’t find the old entry “Digital Wellbeing” in the corresponding settings of your device. This is now called “Digital Wellbeing & parental controls” and gives you access to the family link features (the app will be installed automatically if necessary), like setting time limits for individual apps and so on. Your children should also be able to use the Family Link interface to request an extension for an app, which you can then agree to or disagree with.