Recently, Niantic has provided the ability to enable sponsored Pokestops and Gyms for child accounts using Niantic Kids
If your child logs into Pokémon GO using Niantic Kids, you can opt into enabling sponsored content for your child in the Niantic Kids Parent Portal, which will allow your child to be able to interact with sponsored locations.
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At this time, this functionality is only available for Niantic Kids accounts. We hope to make it available to Pokémon Trainer Club accounts in the future.
This is intended. PokéStops and Gyms at sponsored locations are hidden from those who are under the age of 13
Sponsored locations (branded PokéStops and Gyms created through partnership agreements with Niantic) are only available to Trainers ages 13 or over. Trainers under the age of 13 are not able to see or interact with sponsored locations.
Niantic wrote a blog clarifying this on 12/14/2016, which I found was in response to a letter from Campaign for a Commercial Free Childhood on 12/13/2016