In our parish, we use adult servers for daily and funeral masses, but children for all weekend and holy day masses.
I coordinate the young servers for my parish, and am a bug on training, and scheduling new servers with more experienced servers. In fact, I took over this job for exactly that reason - my son became a server and never received any guidance or training. So I wrote a manual based on the GIRM (not much there for servers, actually) and insist that my servers learn the parts of the mass, and why their participation in it is so important.
I grew up in the age of felt-banner catechesis, and learned my faith serving at the altar from a dedicated young priest who took us in hand and taught us not just the rubrics, but what they symbolized, and why they are important. It was one of the most important experiences of my life, and I am dedicated to giving that same experience to the children in my parish.
In fact, I have a training session tonight (and last night) for the new servers we gained at “sign-up Sunday” a few weeks ago. Within a month these young kids will be on the schedule and serving at the altar of the Lord, just a few feet from the greatest miracle ever known. And they will know and understand it, and be proud to participate in it.