Rule one of having a useful intern experience is to get them writing production code as quickly as possible. They check in their first change? Get that thing into production immediately. (If it's going to destabilize the system, why did you approve the CL? You two probably pair programmed the whole thing together.)

I completely agree- even if it's something small.

I'm an intern in a big company with an internal robotics and automation group, and I recently got to wire up a pretty basic control panel, install it, and watch workers use it. That was so cool, and made me appreciate what I was doing a lot more.

Sure. The interns have their own branch, but it doesn't stop them from being disruptive to the human in charge of mentoring them.

All changes should be in a new branch.

I used to believe this. Having solid lower environments which are identical to production, receiving live traffic where engineers can stage changes and promote up removes some of the “all things should live on a branch” business. I know that sounds crazy, but it is possible for teams of the right size to go crazy on master as long as the safety nets and exposure to reality are high enough in lower environments.