There is some merit to that, but not quite in the way you may believe. Their “boot camp” (that didn’t actually teach much in the way of combat, just enforced the Spartiates’ social hierarchy) did involve the senior children abusing the younger ones (including sexually), creating a shared suffering and an incentive to become the fucker rather than the fucked.

You’re more likely to fight harder alongside the people that made it through the same awful shit as you did.

If you’d like more info, there’s a historian’s blog I very much recommend who wrote a series on Sparta.