Okay, admittedly I don't have any experience actually trying mirrors, but what people are saying just doesn't make physical sense to me. Aluminum foil is bad because the crinkles create hot spots. This makes sense to me. The small creases that you can't avoid will create many small focal points where a large amount of light is focused down to a small point (which could burn your girls). But if you have actual flat mirrors, these should just reflect the light specularly (incident angle=reflected angle). In other words, the light should not converge to tiny harmful focus points (unless you for some reason used odd curved mirrors. I believe if you used planar flat mirrors as your walls you'd be in great shape. (although I doubt the performance of mirrors over flat white paint would make up for the increased cost if money was any issue.) Certainly though, I'd be very curious to hear from anyone who has any actual experience using mirrors as walls...
