DD was different from birth. The only reason that it took us a while to figure this out is that:
1. My DH and I neither one are "kid" people-- and we didn't spend much time around other babies or toddlers, and when we did--
2. Family and colleagues were mostly at least MG, so this also wasn't necessarily a good measuring stick, either-- but DD was still different-enough-even-from-that-cohort that people other than us were noticing pretty early on.
We didn't think all that much of it until she was more like 2yo, though, and was doing things that NO 2yo should/could do. Not even "very bright" ones. She was a little bit alien-- it was very disconcerting, but one only saw what she wanted to show, too, so it was also quite uneven and generally ocurred in flashes.
I do recall being somewhat bemused by friends who were, say, horrified that we never needed childproof anything in our house, though-- but by the time DD was mobile at 6-10mo, she was rational enough that all we ever had to do was explain why things were a bad idea. It took me a long time to realize that other children were irrationally impulsive as toddlers and preschoolers. DD wasn't.
