It would depend on the size you used as to whether or not they did what you said. The equivalent chainring size makes them smaller during the "weaker" parts and larger during the drive. So a 53 is equivalent to a 56 at the big point and 50 at the smallest (it depends on which setting you use). So if you sized down (say a 50 QRing), then you could make it so the biggest they ever got was as big as your normal ring and the smaller was much smaller. However, then you would be further reducing the overall gear inches, and since the kids are on shortened roll-out anyway, that doesn't seem like a useful idea.
Read any of Ed Burke's books, all of which cover the subject. Ovoid change rings are best for low-cadence, high-power pedaling, which doesn't seem to me like what you want to be subjecting young bodies to.
Regarding adapatation, they ride on reduced rollout as Juniors, when their bodies are learning. If they ride these rings are Juniors to give them an edge, that is the pedal stroke they will learn. And then if you take them off once they graduate from Juniors, when their bodies are no longer so adaptive, then you have committed them to this equipment. The habits they develop as kids become harder and harder to shake as they get older.
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