It is perfectly fine to serve your client directly in the language of their preference. At the same time, it may still be a good idea to have an interpreter as part of your team.
If you work for a non-profit that serves speakers of languages other than English, you may find yourself using automatic translation to bridge the language barrier. I would like to encourage you to use it appropriately and consider what alternatives may be a better fit in some scenarios.
While it may be harmless or even helpful for the family in many everyday situations, I would warn against relying on child interpreters in high-stakes situations that may have financial, legal, or medical consequences.