When we are conceived we are all born with a specific combination of vata, pitta and kapha. This is determined by our parent’s genetics, diet, lifestyle, emotional state, and the environment. For example, if both parents are vata, and eat a vata dominant diet, and are making love during fall, a vata season, then the child will most likely have a vata constitution.
Taking the example above, if one parent is vata and the other is pitta, but all the other factors remain vata, then the child will be primarily vata but also be pitta secondarily. Keep in mind, when Ayurveda espouses to balance the doshas, this doesn’t mean you should have equal amounts of vata, pitta and kapha. It means maintaining the balance of doshas with which you were conceived.