At her 18-month check-up, DD1 demonstrated to the surprised paediatrician that she could name all the colours he pointed to (I remember "grey" being a particular surprise).
Aged 3, she opened our kitchen door as far as it would go, so it was right back against the wall (i.e. had moved through 180 degrees), then said "Mummy, if I put a piece of chalk under here (pointing to the bottom free corner of the door) then close the door again, it will draw half a circle on the carpet." It took me a while to realise she was right.
There was also the Toast Calculation when she was three. Every morning I used to ask her how many pieces she wanted her slice of toast cut into, and had explained the words (half, quarter etc.) One day she said "I’d like five pieces today, so that will be two quarters and three sixths."
She loved pre-school, played with dolls etc., went to ordinary state primary and comprehensive schools, got 5 top-grade A Levels and has now got an Oxford maths degree. She’s not a terribly sociable person, though, is happy with her own company and finds it hard to make chit-chat.
DD2 was highly competitive so insisted on doing 6 A-Levels (to outdo her sister), aced them all and also went to Oxford. She is much more sociable and sporty and has lots of friends and interests.
I'm not sure I really know the difference between being gifted and "just" being highly intelligent. Either way I wouldn't make a big deal of it. We’ve all seen sad stories about "gifted" children pushed too hard by their parents and ending up as unhappy misfit adults.