About a decade ago, while working for a large a multinational headquartered in Silicon Valley, I had the wonderful experience of working with a bunch of interns; an experience I believe to be very relevant to your current challenge. Working with junior employees, irrespective of their area, can be an extremely rewarding experience, both for yourself as well as for the new hires.

In my case, the interns were made available due to a direct agreement between my employer and a nearby university (SCU). This reduced the costs of an intern, from a budgetary perspective, to zero. This was significant, imho, because most of colleagues who were assigned interns, considered their value to be equal to their costs, which I believe was a grave mistake. I am mentioning this to further qualify my personal experience.

Regardless, even though from a budgetary perspective, the interns were 'cheap labor' I never considered them as such. From my perspective, I had an obligation towards them. My job, with respect to their 1 year internship, was to teach them how to be a professional. The better I was at my job, the more valuable they would be to me and to my company. This was in strong contrast to how my colleagues approached the interns assigned to them. Suffice to say that within months, most interns ended up under my care.

Now - to finally answer your question; I developed a particular approach to educating the interns. Briefly summarized, these were the steps:

(btw: always try to refer to a framework to aid communication, as you can see below)

1. Teach your new hires how to communicate. It is impossible to stress how important this step is. The framework I used was based on a training I had taken my myself and is called SCIPAB. "Situation Complication Implication - Position Action Benefit". What this basically means is, whenever they communication they need to tell what they are talking about (Situation), what the issue is that is making things difficult (complication), why that issue is important (implication), what they think about it (Position), what they think I (or they) should do about it (Action), and why that action will make everything better (Benefit). It helps if you know this framework.
I made them leave me voicemail messages (max 2 sentences) daily for about two weeks training them on how to communicate to me. The benefit to me was that they could communicate efficiently with me.

2. Further I taught them what it meant to be a team member. Group projects at university are a terrible way to prepare people to work in professional teams. I used the Belbin team roles framework to discuss this with them.

3. As the final portion of their initial training, I explained to them the different emotional stages they should expect to experience at work. Elation (at getting the job), Fear (not knowing what is expected, nor how to be successful - fear of failing / impostor syndrome), Depression (finally figuring out what is expected, but struggling to keep one's head above water), Confidence (finally knowing what's expected and how to achieve/exceed expectations. I always added that as soon as they reach the confidence level, I'd immediately 'promote' them so they'd go through the cycle again.

4. On the first or second day they started, I warned them that I would set them up for failure. Even though I told them in advance that it would happen, it still took them by surprise. You have to make your junior employees fail. Failure is a part of life, it is part of one's career. You, as their mentor or manager, have to create an opportunity for them to fail as part of their training. Giving them an opportunity to fail in an environment you control (a failure which does not negatively impact their careers) will allow them to experience the emotions associated with failure and give them the opportunity on learning how to deal with those emotions constructively.

5. As a final point, I had the tendency of implicitly trusting my intern's work. For example, a new intern had joined my team less than three weeks ago. I had gone through the first three steps above and had asked him to prepare a document for me. He had sent me a draft of the document via email and I called him, asking him if the document was ready for review. When he answered 'Yes,' which, of course, it wasn't (the intern was kid - what did he know, right?!) I immediately (and without proof reading) forwarded the document the cross-company team leading my project. The people on that team were of a sufficient level that the interns (and most others on my team) would fear their judgment. Now, my intern (as I expected and I eventually confirmed with others in my team) freaked out completely. Though, in his mind, I ended up with the proverbial egg on my face, from that day forward, he always made sure that whatever document he sent me was either ready for scrutiny, or he would specifically review it with me prior to sending me a copy.

This last point, though it seems added as an afterthought, is truly vital. Your employees will deliver work to the level of trust you give them. If you always insist on reviewing their work, they will give you a product in need of review. If you show them you trust their work, they will make sure that they earn that trust. As a side note, if you implicitly trust them and they fail your trust significantly after the first two or three months of employment, you will have to let them go. (This is a difficult thing to learn as a manager. Sometimes it just simply doesn't work out. It benefits neither you, nor your employee, to avoid the inevitable....)

This is but a brief summary and is hardly detailed. There are many more steps to making a green hire competent and valuable. Getting them to become valuable members of your team is the most rewarding part of being a manager.

Anyway, I wish you all the best on your journey in shaping the new engineers which will make your company great!

EDIT: fixing errors in first draft.