1. The reason people raise concerns about Google, and less so about iOS, is that Google and Apple are in different businesses. Google is in the business of profiting off your personal data and that of your family members. Apple is not, and iOS makes it significantly harder for rogue apps to get access to personal data without the actual user's direct permission.
2. Google (Android) and Apple (iOS) place different priorities on security relative to other factors.
3. Many of the naysayers are raising issues that do not single out Android, however fair it may be to do so. There are some issues that remain the same beyond the specific platform. For example: this kind of app creates social pressure for people to be tracked by their family and show trust that they may not sincerely feel.
4. If you think they can "just" turn the feature off or "just" remove the trusted contacts when they feel uncomfortable, you are not thinking this through. These "trusted" contacts may be authority figures in the family and may be able to examine any settings done by the actual users.
5. If your kids are carrying a cell phone, it should probably be a secure phone, with strictly enforced app store policies, and with a secure OS that is not provided by a company with every incentive to gather and monetize personal and private information. Your kids do not deserve to be the targets of this kind of commercial activity. So even if you think the feature is good, it is tainted by the interests of the provider. But whether the feature is good or bad, Android is a bad way for children to get the feature.