Gifted children

Been reading and watching some documentaries about gifted children, and it just fascinates me. A lot of the times it becomes clear after some years/starting school, because it is not always an easy ride before that or it wasnt that noticable for the parents at first (for example kid acting out very bad because of boredom but parents thought it was just a difficult toddler).

I am interested in that part, to hear from people who themselves are gifted or from people who are parents of a gifted child:

Looking back, what were the things in the first year to 18 months, that pointed out to giftedness? Intellectual + behavioral things