My first-born (now eight) is at least highly-gifted, and I pretty much "knew it" from infancy with her. My youngest is probably highly-gifted too (he's 3.5 years old) but we're still waiting to see how all of that unfolds. I always used to refer to my second-born as our "blessedly average" one (not in front of her -- but when close friends would have some type of unspoken expectation of her because of her older sister, we would make it clear that her achievement levels were in the "normal" range and that we were just as happy and proud of HER as we were of her older sister).
However, a couple of years ago I was talking with a parent of one of my former students who has five kids (now teenagers or adults) who are all highly-gifted or profoundly-gifted. We started off talking about my oldest (who was in kindergarten at the time), but she kept asking about my SECOND daughter. I kept telling her that my second daughter (she wasn't even in kindergarten yet) was academically very normal with all of her milestones like letter and number identification being hit at the "normal" time...but she actually had SOME of the EMOTIONAL characteristics of gifted kids to an even greater extent than my oldest daughter (much more sensitive...a worry-wart...perfectionism...etc.). This other mom just looked at me point-blank finally and said, "You KNOW your second daughter is gifted, right? She may not be reading yet and stuff like that, but she's ABSOLUTELY gifted." I just kinda smiled and nodded...but thought she was just one of those moms of gifted kids who saw giftedness everywhere she looked and just didn't really think much about it.
Well, my second daughter remained "blessedly average" through kindergarten...but her little lightbulb turned on very early in first grade and she finished the year scoring at the 99th percentiles in the math and reading sections of SAGES. She's now performing at a high level in her self-contained full-time high ability class as a second grader. Stinker. :-)
