I don't know. My DD was a very calm baby, but my DS1 was a holy terror, and I probably was the same laidback parent to the both of them.

Charlie is an incredibly active, social, secure and self-assured child, but I would not come close to classifying him as calm, by any stretch of the imagination. Yet while I admit to being a more anxious parent with him than with my other three kids, I am a very even tempered, calm person in general, and so is DH, and Charlie is soooooo not a calm baby.

But there is exceptions to every rule and perhaps we're one of them?