‘Flicking out spikes’ at pace might be quite hard to do with intent, without slowing yourself down too much. And also hard to flick them out far enough you’d be obstructing someone in a different lane. So that sounds a bit odd.
Getting spiked in XC when you run too close together is definitely a thing though (or deliberately trying to scrape the back of someone’s calves in front), ouch… albeit not as bad as a proper shin/pedal impact in my experience.
I was relatively close and saw one incident where the boy in front veered into his line, causing them both to stumble.
The coach should be having a word about that – if the kids are training in specific lanes, the importance of not straying out of your lane (which will get you DQed in a race) ought to be emphasised. Although if it’s just a one off the coach might think, as you say, it’s only a training session and they’re only young so let it slide the once.