Your child was baptized, circumcised, named, blessed, dedicated, or otherwise marked before they could consent. Or they were raised in your secular conviction that none of that mattered, which is also a marking. Either way, you handed them a tradition — including the tradition of having none — and at some point they will examine what you handed them. Some keep it. Some throw it. Most do something stranger and slower: they take it apart and reassemble it into something that is recognizably yours and unmistakably theirs, and they do not always tell you which pieces survived.
The temptation is to read their examination as a verdict on you. It is not. James Fowler's stages-of-faith framework, whatever its limitations, captures something experientially true: there is a predictable adolescent and young-adult passage from synthetic-conventional faith (the faith of belonging, of "this is what we do") to individuative-reflective faith (the faith of personal accounting, of "this is what I have decided"). The passage is not optional and not a failure. A child who never enters it has not preserved your faith; they have only postponed the encounter, and the postponement usually costs more than the encounter would have.
The hardest thing for a religious parent is that the child must be free to leave for the staying to mean anything. A faith retained only because departure was unsafe is not faith; it is captivity dressed in vestments. The hardest thing for a secular parent is the inverse: the child must be free to find God, and if they do, the parent's job is not to roll their eyes at the prayer group. Both forms of parental anxiety share a structure — the fear that the child's choice will retroactively unmake the parent's life.
Practical posture first. Tell them what you actually believe and why, including the parts you are uncertain about. Children raised on the performed certainty of parents who privately doubt smell the gap and respond either by replicating the performance (and breaking quietly in their thirties) or by repudiating the whole apparatus (and breaking publicly in their twenties). Honest uncertainty about specific claims, paired with clear commitment to specific practices, is more transmissible than false confidence. You are not weakening their faith by admitting you do not know whether the universe is friendly. You are showing them that an adult can hold a tradition while still asking questions, which is the only kind of holding that survives an education.
Take their questions seriously, including the ones designed to provoke you. A fourteen-year-old asking why God allows suffering is not trolling; they have noticed something real, and the theological tradition has been working on it for three thousand years. Hand them the better answers, including the answer that the question may not have an answer and that the practice goes on anyway. Do not, under any circumstance, treat doubt as a sin. Doubt that is forbidden becomes doubt that is hidden, and hidden doubt is what calcifies into the silent atheism of the still-attending adult.
If they leave, do not stage a crisis. The most reliable way to lose them permanently is to make their return contingent on confession. The most reliable way to keep the door open is to let them know that the table is set and they are welcome whether they are praying or not. Andrew Solomon's work on horizontal versus vertical identities is useful here: a child whose spiritual identity diverges from the parent's is in some ways like a child whose sexuality or neurology diverges — the parent's task is to love a person they did not anticipate, in a future they did not script.
If they stay, do not exhale. A child who keeps your faith without examining it has done you a courtesy but not a service. Push them gently toward the texts and teachers that will trouble them productively. A tradition strong enough to be inherited is strong enough to be questioned, and a tradition that cannot survive questioning was not strong enough to inherit in the first place.
The unity at stake is not unity of belief. Two people with identical creeds can be strangers; two people with different creeds can be kin. The unity is the unity of a relationship that has metabolized the fact that the soul next to yours is not a copy of yours and was never going to be. Your child's faith, examined or unexamined, kept or discarded, will be theirs. Your job was never to make them believe what you believe. It was to give them something worth examining and the courage to do the examining honestly.