Brian A. Dewhirst mentioned in a post on the OOC list for Jvstin's Strange Bedfellows campaign that, "only an exceptional woman can bring an exceptional child into this world."
Some of the general assumptions made in regards to why Oberon went through a stack of wives ("Fourth wife, put her into a bag. Fifth wife, into outer space. Sixth wife, on a Rotissimat. Seventh wife, made out of jam...") seem to suggest that women of Shadow have a difficult time in bearing Real children.
I have a different method.
When someone Real is born in Shadow, that Real Child may not seem anything beyond the ordinary. Sure, they might be Olympic-level. They might have the few oddities, but that's maturity speaking. It's not until that Shadow is touched (Primal Power, Pattern, Logrus, whatnot) that the latent Reality is opened. Think of Power as a key. So, presumably an son or daughter of Reality could live out a full life in a Shadow. I'd suggest it would probably be a fairly full life, as the Shadow would have been touched by the Real person in that Child's conception at the very least.
I extend this to Travel through Shadow as well; the more travelled you are, the more you activate your powers. This includes Shadow sourcerors as well as the Real; knowledge of how to step through to other worlds indicates generally a level of Power. The limit? YMMV.
This may also lead GMs to consider that Chaosians, who presumably have the benefits of very thin Shadow walls (depending on which canon interpretations you select) may grow into their Power faster, perhaps requiring Shapeshifting from a very early development point.