What professional guidance can I provide to junior enlisted to help them grow?

Love me books!
If you don't have one, build one.
Getting them while they're young is ideal for Love me book creation. It makes preparing for the admin side of promotion boards straight forward and can highlight areas in your career that you might be lacking in.

Look at your career and experiences to see what you have learned and where you would like to have seen someone teach you. Professional development such as correspondence courses and civilian education are big. Learning SOPs and other office procedures is important. Then look at leadership. In my career I have been disappointed many times by leaders who were simply promoted because they had the points but showed no real leadership quality. Teach them how to lead training related to your MOS and basic Soldiering skills. Teach them how to counsel by conducting various simulated positive and negative counseling session. Teach them about the UCMJ. Seek the help of other leaders around you within and outside of your MOS for ideas or training plans. In basic training we were given a "smart book" and any down time we were told to conduct hip pocket training. Think that way. What should they know? What do you want them to know? Do they know the chain of command or the structure of the command? Give them a scenario and see how they would handle it. Be a leader they trust and want to learn from.

You should research what they provide during in processing and expand on that. They should cover college, and some self development opportunities. You mention that MOS wise things are a little slow. Take that opportunity (with supervisory approval) to bring them up to speed in unit SOP’s advancements in your field, etc.