This may get me in some hot water, but I'm going to stand by this statement:
Youth Strength Coaches should teach young athletes how to deadlift with a straight bar, and utilize it in training in some form, in order to lay the best framework for later athletic development.
Now with that said, let's lay down the context for this conversation and why I think we shouldn't be avoiding this deadlift variation. This conversation also may apply to private sector Strength Coaches more than others, especially those who work with middle and high school athletes who don't have qualified strength coaches in their schools. Let it also be said that I do believe the trap bar deadlift is easier to teach and that it should also be taught. I do in fact believe it should be taught first, but at some point we should teach young athletes to deadlift with a straight bar.
But something I think many forget when tossing the straight bar deadlift out the window is the other weight room influences their young athletes may have or will have later on. I had to realize this in the past few years working with athletes who trained with me outside of their team lifts, as well as visiting the schools they were training in to assess what was going on in the weight room. This part of the context is important: very few high schools in my area use or even possess trap bars to deadlift on (in my geographic region, roughly 30% of the schools have trap bars), but all of them deadlift or use the Olympic lifts.*
This may sound arrogant, but one thing I realized very quickly by visiting these schools and working with the athletes coming from these weight rooms is that I could teach a straight bar deadlift far better than what kids were being taught in the schools. And to add to this, I feel like coaches who choose trap bar deadlifts over straight bar could probably still teach kids how to deadlift and save them more risk for when they are in they're local school deadlifting.**
I also think that as a coach for youth athletes, one of the responsibilities we carry is to prepare them for whatever comes next. Young athletes grow up into the next generation, and if we steer clear of certain things in the weight room that may be presented of them we may setting them up for a weaker future. What if they play college sports and their new strength coach has them straight bar deadlifting? You're putting them at an advantage to succeed under that coach. What if they join a gym as an adult, where trap bars aren't available and they still want to deadlift? You can provide that opportunity.
Now I understand that trap bar deadlifts are easier to teach, as are KB deadlifts, and they are less risky because of the loading patterns. Personally, I always start with the previously two mentioned variations, but at some point the straight bar has to be taught in order to keep them safe long term. You don't necessarily have to use it in a training program, but teaching it as a skill has a value that extends beyond the bubble you share with your athlete.
I would also suggest that you teach multiple variations of the straight bar for your young athletes. Teach conventional deadlifts, clean deadlifts, and sumo deadlifts. Being proficient in these, even if it's just for motor learning can have a lasting impact on the preparation of a young athlete!
*This is based on my experience working with local schools and their athletes, but this may be a slight geographical bias.
**I also understand that there are a lot of great high school strength coaches who are making profound impacts for coaches all over, but I believe that they are still currently a minority among the total number of coaches teaching things in the weight room