Parents in the UK will some times describe a child as "flirty", it has nothing to do with sexuality - to head that one off. They have learnt, by only a few months old, to attract attention of adults by using facial expressions, coos, and such. They certainly seem to be the other end of the spectrum wrt commanding social interaction.
But I'd suspect it's more that most children have the capacity but a few just happen upon the formula early. Like we mostly have capacity to walk but some take 14 months then just get up and walk, whilst others are walking at 8 months when they can barely raise their heads; and others are crawling backwards, or shuffling on their bums because walking didn't click quite so quickly.
Myers-Briggs type theory suggests that there are 8 modes of cognition, and that we all develop one first and only later begin to develop the others. Even if you don't like the Myers-Briggs stuff, I think the idea that children all develop a specific way of thinking first, but that the one that develops first isn't the same for all children is insightful.
But I'd suspect it's more that most children have the capacity but a few just happen upon the formula early. Like we mostly have capacity to walk but some take 14 months then just get up and walk, whilst others are walking at 8 months when they can barely raise their heads; and others are crawling backwards, or shuffling on their bums because walking didn't click quite so quickly.