Or, like some aspects of "essential nature" that do not manifest until puberty*, it may not be so, remaining undetectable until the child matures (depending on the exact nature (small "n") of the Gift). As a SG, I prefer not to paint myself into a corner with hard "always does/never does" rulings, and whenever reasonable to create a "...There are several schools of thought..." environment to keep all options open for different story lines, for myself and co-SG's. (Same with "How do demons/ghosts/undead/faeries work?" questions, etc.)
I think this would be one of those times. The only concern is that the game-world not be self-contradictory, and "It is not perfectly understood" usually covers that best.
(* Is it within the "essential nature" of a healthy newborn to bear/sire children? Ymmv...)
Or Hearing - in a crowded environment, in a city with walls, it's often easier to hear a small child than spot them, especially through a shuttered window or behind a garden wall. Or just Touch, to personally verify a suspected Gift.
But it's not easy - InVi Base 5, +2 Sun, +4 Sight = Lvl 35 - not something that is going to be easily spont'ed, nor invented without some dedication in that direction. Anything less than Level 30 (Sun, Hearing) means that it's only going to be used when the Gift is suspected - and we're back to first finding those suspects the old-fashioned way.
But it's the same with any spell that "solves" a common problem - flying solves travel, invisibility solves sneaking, illusions solve anonymity, etc. etc. Yet none of those "solutions" are foolproof (far from!). A mage should be able to do "powerful stuff", and not expect punishment from the Dungeon Master just because they can take a shortcut within their arcane specialty.
And even then, not every Gifted child is apprentice-worthy, and telling the difference is often a bigger challenge (and headache!) than finding one to begin with. The flaw can be in the Gift, or in their personality - destroying an apprentice can be a great storyline in itself (tho' I, for my style of SG'ing, would be cautious which Player I hit with that particular club, and would make sure to balance that lost effort with some major carrot.)
In the end, it's still 100% up to the SG, and all about what makes the best story, for the Saga, for the Troupe and for that Player and Character. Sometimes, a Player is far less interested in RP'ing the finding of the apprentice than in the challenges of training/molding them - and that's where the perceptive SG should handwave the first part and focus on the interaction between Parens and Apprentice.
Not if you allow forceless casting.
But even then, it's also not guaranteed that "victim" would notice - having the PC stress about the possibility of censure might be more fun than hitting them with it.
And even then, most Tribunals (and most magi?) recognize (and usually acknowledge) accidental scrying as less offensive than deliberate - it's the difference between an accidental foul and an intentional one - the former gets you a penalty, but usually only the latter can get you ejected from the game. 
