General advice: Avoid power fights. They are pointless, use valuable resources and burden relationships.

The only reason to impose rules on others — including our children — at all, in my view, are the same as in our society of free citizens at large:

• Because parents are responsible for the well-being of their children they must prevent behavior that poses a significant risk to the children themselves. That is something that the general laws only do occasionally — we are allowed to free climb or base jump but we may keep our children from doing it.

• Parents should prevent behavior which impinges on others' rights, including the right to be left alone and not be disturbed or annoyed. This includes, as an extreme case, putting others in danger.

The second point is the same very general principle that governs the laws we live by, starting with the constitution: We try to balance the right of the individual to live their life as they see fit with the potential negative impact of that conduct on others. It is perhaps surprising to some that I apply this principle to children but I think they too are essentially free individuals, to the degree possible. That the self-determination is not as all-encompassing as for adults does not change the general idea.

We can discuss this principle along this concrete example. For whatever reasons, your son likes to have his shirt untucked. Does this impinge on others' rights or well-being? To be honest, not really; but as others said, it may violate social norms, even at home. If that makes people who see the sloppy dressing really uncomfortable it may be a reason to tuck it in; but one could also argue that they are overly sensitive and that your son's right to dress as he pleases has a higher value. Which side "wins" in this balancing is not immediately clear; we should probably be more considerate of grandpa than of arbitrary strangers who don't like sloppy dressing. If grandpa insists and your son refuses he must stay at home.

The issue would be different if your son insisted on being naked; nudity is still a strong taboo. It is hard to argue that anybody is hurt by looking at a nude person, and indeed, for that reason legal challenges arise occasionally against an obligation to be dressed in public. But it is a fact that nudity elicits strong emotions that some people find uncomfortable, and for that reason alone it is considerate to not be nude in public after the age of three or so.

Of course, as other answers have rightly recommended, it is an important part of a child's (an, indeed, anybody's) education to make them aware of social norms, non-verbal communication, different social contexts (funeral vs. party) etc. A valid reason to ask the child to dress properly is also if that sloppy dressing is embarrassing to the parents. The degree of embarrassment again depends on the occasion; often I'd simply recommend to shrug and ignore it.

General advice: Avoid power fights. They are pointless, use valuable resources and burden relationships.

The only reason to impose rules on others — including our children — at all, in my view, are the same as in our society of free citizens at large:

• Because parents are responsible for the well-being of their children they must prevent behavior that poses a significant risk to the children themselves. That is something that the general laws only do occasionally — we are allowed to free climb or base jump but we may keep our children from doing it.

• Parents should prevent behavior which impinges on others' rights, including the right to be left alone and not be disturbed or annoyed. This includes, as an extreme case, putting others in danger.

The second point is the same very general principle that governs the laws we live by, starting with the constitution: We try to balance the right of the individual to live their life as they see fit with the potential negative impact of that conduct on others. It is perhaps surprising to some that I apply this principle to children but I think they too are essentially free individuals, to the degree possible. That the self-determination is not as all-encompassing as for adults does not change the general idea.

We can discuss this principle along this concrete example. For whatever reasons, your son likes to have his shirt untucked. Does this impinge on others' rights or well-being? To be honest, not really; but as others said, it may violate social norms, even at home. If that makes people who see the sloppy dressing really uncomfortable it may be a reason to tuck it in; but one could also argue that they are overly sensitive and that your son's right to dress as he pleases has a higher value. Which side "wins" in this balancing is not immediately clear; we should probably be more considerate of grandpa than of arbitrary strangers who don't like sloppy dressing. If grandpa insists and your son refuses he must stay at home.

The issue would be different if your son insisted on being naked; nudity is still a strong taboo. It is hard to argue that anybody is hurt by looking at a nude person, and indeed, for that reason legal challenges arise occasionally against an obligation to be dressed in public. But it is a fact that nudity elicits strong emotions that some people find uncomfortable, and for that reason alone it is considerate to not be nude in public after the age of three or so.

Of course, as other answers have rightly recommended, it is an important part of a child's (and, indeed, anybody's) education to make them aware of social norms, non-verbal communication, different social contexts (funeral vs. party) etc. A valid reason to ask the child to dress properly is also if that sloppy dressing is embarrassing to the parents. The degree of embarrassment again depends on the occasion; often I'd simply recommend to shrug and ignore it.