Sponsored locations (branded PokéStops and Gyms created through partnership agreements with Niantic) do not appear in the game for Trainers with child accounts, by default.
 

Opting Into Sponsored Locations

If your child logs into Pokémon GO using Niantic Kids or Pokémon Trainer Club (PTC), you can opt into enabling sponsored content for your child in the Niantic Kids Parent Portal or Pokémon Trainer Club website, which will allow your child to be able to interact with sponsored locations. Sponsored game content is in-game content that features external companies as a form of promotion. This could include sponsored in-game locations or sponsored in-game items or gameplay. For example, branded PokéStops and Gyms created through partnership agreements with Niantic. Niantic does not share your child’s personal information with sponsors and opting into this feature won't change that. You can also revoke your child’s access to sponsored content at any time.
 
Note: Child accounts will not receive Sponsored Gifts, even if permissions for accessing sponsored content are granted through the Niantic Kids Parent Portal or Pokémon Trainer Club website.