The "best interests of the child" standard -- the standard rule applied in custody disputes between two parents -- leaves family court judges ample room to consider a parent's ideology. Parents have had their rights limited or denied partly based on their advocacy of racism, homosexuality, adultery, nonmarital sex, Communism, Nazism, pacifism and disrespect for the flag, fundamentalism, polygamy, or religions that make it hard for children to "fit in the western way of life in this society."
Courts have also penalized or enjoined speech that expressly or implicitly criticizes the other parent, even when the speech has a broader ideological dimension. One parent, for instance, was ordered to "make sure that there is nothing in the religious upbringing or teaching that the minor child is exposed to that can be considered homophobic," because the other parent was homosexual. Others have lost rights based partly on telling their children that the other parent was damned to Hell. One mother was stripped of custody partly because she accurately told her 12-year-old daughter that her ex-husband, who had raised the daughter from birth, wasn't in fact the girl's biological father.
Courts have also restricted a parent's religious speech when such speech was seen as inconsistent with the religious education that the custodial parent was providing. The cases generally rest on the theory (sometimes pure speculation, sometimes based on some evidence in the record) that the children will become confused and unhappy by the contradictory teachings, and be less likely to take their parents' authority seriously. This article argues these restrictions are generally unconstitutional, except when they're narrowly focused on preventing one parent from undermining the child's relationship with the other. But the observations that lead to this rule are likely, I think, to prove more interesting to readers than the rule itself:
(1) The best interests test lets courts engage in viewpoint-based speech restriction.
(2) The First Amendment is implicated not only when courts issue orders restricting parents' speech, but also when courts make custody or visitation decisions based on such speech.
(3) Even when the cases involve religious speech, the Free Speech Clause is probably more important than the Religion Clauses.
(4) If parents in intact families have First Amendment rights to speak to their children, without the government restricting the speech under a "best interests" standard, then parents in broken families generally deserve the same rights.
(5) Parents in intact families should indeed be free to speak to their children -- but not primarily because of their self-expression rights, or their children's interests in hearing the parents' views. Rather, the main reason to protect parental speech rights is that today's child listeners will grow up into the next generation's adult speakers.
(6) Attempts to limit restrictions to speech that imminently threatens likely psychological harm (or even cause actual psychological harm) to children may seem appealing, but will likely prove unhelpful.