My junior high track days are well behind me but unless your kid is competing at a high level, spikes are not really common. I would consider avoiding the gear trap and just see how it goes in regular trainers.
More accurately it is not uncommon to see kids in running shoes at the 6, 7, 8th grade level. However, spikes are pretty normal for most of the sprinters and jumpers.
My kids (girls BTW) wore spikes for cross country right from the start, some time around the age of 10. Again, not unusal to see kids in running shoes, but most had spikes.
As a high school and college sprinter (200/400 or 220/440) my heal never touched the ground between getting in the blocks and hit the finish line.
Which reminds me - The memories of cinder tracks and 3/4 inch spikes, cotton sweats, 6 parents with sweep hand wind up stopwatches, and blocks that had a 4" spike at each end that was pounded into the track with a rock and still had to be stood on by the shotputter to hold them down.
Remembering back, in middle school, most kids did not have spikes. But quite a few did.
In high school, almost everyone did. Except those that didn’t care at all for it. Even the poor kids (me) had spikes.
In Cross country, it was ~50/50. All of our varsity runners had spikes though, even the one poor kid.
Totally different shoes. We were also limited to 3/8" spikes on tracks - the nicer rubberized tracks were just starting to roll out, ours was asphalt. 3/4" to 1" were pretty common for CC, half the fun was trying to match spikes to the course and weather 
But the first time your kid slips, he’ll come asking for spikes. Check out firsttothefinish.com - that’s where I got the pictures above. They’ve got a good supply of closeout spikes in the ~$20 range if they’ve got his size.