My experience from a place with a lot of junior developers:
- People without formal computer science education but with some amount of practical programming experience follow a 6-week full-time training (not everyone makes it). There are big experience differences and the learning style isn't perfect, but it does help prevent most language-level questions.
- New people are assigned a mentor who they can ask questions to. In the first weeks, this mentor spends a non-trivial amount of time each day answering questions. There is generally a realization that this is more efficient for the team that having people spending days trying to figure things out alone.
- When someone else is more familiar with the subsystem or technology, the new employee is directed to that person instead.
- Functional questions are answered by designers, product and configurations questions can often be answered by testers. It's not only a developer thing.
- There are trainings about specific topics (both technology and product-related), and it is encouraged to do one each quarter.
- There are code reviews, which besides protecting quality, are also a good way to learn from mistakes and adapt the coding style.
It is going to take quite some time, which is the price you pay for hiring less experienced people. I imagine it's a new positive, but I've not seen the numbers.
In my experience, a lot of the questions are about the product rather than technical details.
People don't ask me many questions though, so maybe I'm not the perfect person to answer...