people should take pre-existing values and traditions about liberalism and reason seriously, and apply those to all their relationships (friends, coworkers, parent-child, etc).
you value the pursuit of happiness? why won’t you help your kid pursue his happiness, now?
you value freedom, and each person choosing his own way in life? why, exactly, should there be an exception for children? whatever you answer, be super clear about the limits of the exception, and how the same reasoning won’t apply in other cases.
you think children are stupid and need to be controlled by their betters? what’s the difference between this and other authoritarian views? why is this authoritarianism more rational or less cruel? why does it apply by age rather than by IQ test or by having psychologist-kings interview everyone and decide who is competent to run their own lives?
why do you think it’s OK to take your child’s phone away as a punishment? is it his property, or not? do you respect property rights, or not? if you think your answer is that your child is not a property owner, you’re just lending him stuff, then why do you think that’s a good model for dealing with children but property ownership is a good model for the rest of society?
how do you think about voluntarily persuading others and what your options are if they disagree? why don’t you apply similar thinking about consent, persuasion and voluntary action to dealing with your child?