Love for parents...

Duties of children towards parents
Children have a threefold obligation of love, reverence, and obedience toward their parents. This is enjoined by the virtue which St. Thomas calls pietas, and for which the nearest English equivalent phrase is "dutiful observance". As religion makes it obligatory for us to worship God, so there is a virtue distinct from all the others which inculcates the attitude we ought to hold towards parents, in so far as they in a secondary sense are the principles of our being and of its regulation. The violation of this obligation therefore is reputed a grievous sin unless the smallness of the matter involved make the offence a venial one. Of the obligations referred to, love and reverence are in force during the parents' lifetime. Obedience ceases when the children pass from under the parental authority. The duty of love of parents, strongly intimated to the conscience by the natural law, is expressly emphasized by the positive law of God. The Fourth Commandment, "Honour thy father and thy mother", is universally interpreted to mean not only respect and submission, but also the entertaining and manifestation of affection they deserve at the hands of their children.
Those children are guilty of grievous sin who habitually exhibit towards their parents a heartless demeanour, or who fail to succour them in serious need, either bodily or spiritual, or who neglect to carry out the provisions of their last will and testament in so far as the amount devised will permit. It is not merely the external bearing which has to be governed. The inward sentiment of affection must be deep-seated. The Christian concept of parents as being the delegates of God carries with it the inference that they are to be treated with peculiar respect. Children incur the guilt of grievous sin who strike their parents, or even raise their hands to do so, or who give them well-founded reason for great sorrow. The same is to be said of those who put their parents in a violent rage, who curse them or revile them, or refuse to recognize them.
Besides the parental relationship and dignity account is to be taken of their authority. Children, so long as they remain under its yoke, are bound to obey. This does not mean, according to the teaching of St. Thomas that they must intend to do what is commanded precisely because it is enjoined; it is enough that they be minded to do what is prescribed. This obligation covers all those matters and those only which make for the proper rearing of the offspring. Parents have no power to order their children to do what is sinful, nor can they impose upon them against their will any particular calling in life. Theologians find their criterion for determining the grievousness of the sin of disobedience by scrutinizing the command given as well as the matter with which it is concerned. They say that the offence is then to be rated as mortal when the communication of the parental will takes the form of a real precept given in earnest and not merely a counsel or exhortation. They further require that this behest should have to with something important.
There is no hard and fast rule to gauge the gravity of the matter in which an infraction of the duty of obedience will become a mortal sin. Moralists declare that this valuation must be made by the good sense of thoughtful persons. They add that in general when an act of disobedience is calculated to work serious harm to the parents, or interfere seriously with domestic discipline, or put in jeopardy the temporal or spiritual welfare of the children themselves, it is to be accounted a mortal sin. When the thing for whose performance or omission the parent's command is issued is already binding under pain of grievous sin, either by the natural or positive law, the setting at naught of the parental injunction does not involve a distinct sin of disobedience requiring a separate accusation in confession. The reason is that the motive of the command is assumed to remain the same in both cases. An example in point would be the defiance of an order given by a parent to a child to assist at Mass on Sunday, something which the latter is already bound to do.