For child accounts the trust might extend to blocking purchases in the general case and having the kids send purchase requests to the parent for approval.
Of course this leaves the child account restricted is such a manner it would be unappealing if there wasn't an actual parent-child relationship IRL.
For Google Play the requirements are:
I only have direct experience with managing a kid under 13, in that case I have created the account for him and never entered a payment method on his account. For any purchases he wants to make via the "family wallet" it needs my direct approval, which can be granted by using an app on my device or directly entering my password onto his. After either of us has made a purchase we have a "share with family library" toggle that can share the title with the other family member. Note that this only applies to direct title purchases from the store, if a feature is locked behind IAP it can't be shared. We have his accompanied locked so he needs my approval for any purchases (including free apps) but this is not required by the platform.
For child accounts the family manager can choose between requiring approval for each of the following on each child account:
I presume the for adult family members the family manager only has control of the Family Wallet but I don't have direct experience to confirm.