There isn’t any information about this on the ITF’s junior website.
But if you go to enter a junior tournament via their iPin system, you’ll see the big news.
Beginning in 2018, the ITF will be experimenting with the no-let serve on its junior circuit and in its team competitions.
It’s already done in men’s college tennis. And it was experimented with at the Challenger level awhile back.
And, of course, it was famously used at the Next-Gen Finals in Milan.
This time, it’s the kids who will be the guinea pigs.