Presumably this is because apps could add individual features parents don't approve of between updates.
If you're locking down what apps you want your kids to use (to an individual whitelist of apps, not just by maturity rating), you're essentially stepping into the role of an enterprise MDM IT department, auditing software updates for stability before letting them go out.
What would you propose instead here?
I presume you'd personally just be willing to trust certain apps/developers to update their apps without changing anything fundamental about them. But I think that most people who are app-whitelisting don't feel that level of trust torward apps/developers, and would want updates to be stopped if-and-only-if the update would introduce a new feature.
So now, from the dev's perspective, you're, what, tying automatic update rollout to whether they bump the SemVer minor version or not? Forcing the dev to outline feature changes in a way that can be summarized in a "trust this update" prompt notification that gets pushed to a parent's device?