Every legal system must answer an uncomfortable question: at what point does a child become capable of making decisions that bind them? The answers reveal profound disagreements about human development, parental authority, and the proper role of the state.

Some jurisdictions draw bright lines—you're a child until midnight on your eighteenth birthday, then suddenly an adult. Others reject this fiction entirely, asking instead whether this particular child understands this particular decision. Neither approach is obviously correct, and both carry significant risks.

The stakes are highest in three domains: medical treatment, where life and bodily autonomy intersect; contracts and property, where economic vulnerability meets developing judgment; and family proceedings, where children's voices may determine their own futures. Comparing how different legal systems navigate these tensions reveals not universal truths, but the values each society has chosen to prioritize.

The simplest approach to children's legal capacity is the bright-line rule: pick an age, and apply it uniformly. In most of the United States, you cannot consent to medical treatment until eighteen. In most of continental Europe, eighteen marks the transition for contracts and property. The appeal is obvious—clarity, predictability, and ease of administration.

But bright-line rules rest on a legal fiction that everyone recognizes as false. A seventeen-year-old the day before their birthday is not meaningfully different from the adult they become at midnight. Some fifteen-year-olds demonstrate greater maturity than some twenty-five-year-olds. The rule treats unlike cases alike, sacrificing accuracy for simplicity.

The alternative emerged most influentially from the English courts in Gillick v West Norfolk (1985). Rather than asking "how old is this child?" the Gillick competence test asks "does this child have sufficient understanding and intelligence to fully comprehend what is proposed?" Australia, Canada, and New Zealand have adopted variations. The assessment is individualized, decision-specific, and theoretically more accurate.

Yet competency tests create their own problems. They're expensive to administer, requiring professional assessment rather than checking a birth certificate. They introduce uncertainty—neither child nor third party knows in advance whether a decision will be binding. And they invite inconsistency, as different assessors reach different conclusions about the same child. The choice between systems is ultimately a choice between different types of errors.

Takeaway

The debate between fixed ages and competency tests reflects a fundamental trade-off: accuracy about individual capacity versus predictability and ease of administration. Neither approach eliminates the risk of treating children as more or less capable than they actually are.

Medical decisions expose the sharpest tensions in children's legal capacity. The body is the site of the most intimate autonomy, yet medical choices can produce irreversible consequences. Different jurisdictions have reached strikingly different conclusions about where to draw lines.

The Gillick case itself concerned contraceptive advice for under-sixteens without parental knowledge. The House of Lords held that parental rights exist for the child's benefit and diminish as the child's own capacities develop. A child who understands the nature and implications of treatment can consent. This principle has since been applied across common law jurisdictions, though its scope remains contested.

Consent and refusal, however, are not symmetrical in most systems. English courts have repeatedly overridden competent minors' refusal of life-saving treatment, even while accepting that the same minor could consent to that treatment. The reasoning—that protecting life outweighs autonomy for those not yet fully adult—reveals that "competence" alone does not settle the question. The Netherlands and Belgium, by contrast, have extended even end-of-life decision-making to minors under specific conditions, prioritizing consistency in recognizing developing autonomy.

Particularly contested are decisions with permanent consequences: gender-affirming care, psychiatric medication, participation in research. Some jurisdictions have responded by adding procedural safeguards—judicial approval, multiple assessments, waiting periods—rather than categorical prohibitions. Others have moved toward higher age thresholds specifically for these decisions, creating a patchwork where the same teenager might be competent for one medical choice but not another.

Takeaway

Medical autonomy reveals that competence is not the only value at stake. Legal systems consistently treat consent and refusal differently, and add safeguards for irreversible decisions, suggesting that protecting children from harmful choices remains a competing priority even when they demonstrate understanding.

When courts decide custody, adoption, or child protection matters, they must somehow account for the child's own perspective. But how much weight should that perspective carry? Here too, legal systems diverge significantly.

The UN Convention on the Rights of the Child requires that children capable of forming views have the right to express them in judicial proceedings, with due weight given according to age and maturity. But "due weight" is not "decisive weight." Most systems treat children's preferences as one factor among many, declining to make children the arbiters of their own custody arrangements.

Some jurisdictions give greater voice through procedural mechanisms. In Germany, children over fourteen have a right to be heard directly by the judge in custody matters. In Scotland, children twelve and older are presumed mature enough to instruct their own solicitor in Children's Hearings. New Zealand's Family Court may appoint a lawyer specifically for the child, distinct from both parents and the court. These mechanisms don't guarantee that children's preferences will prevail, but they ensure those preferences enter the decision-making process directly.

The underlying anxiety is whether children can distinguish their genuine interests from parental influence or manipulation. A child who expresses strong preferences for one parent may be reflecting genuine attachment—or successful coaching. Legal systems have developed various responses: in-camera interviews, specialized assessors, distinguishing between wishes and underlying needs. None fully resolves the epistemological problem of accessing what a child truly wants, separate from what they've been encouraged to say.

Takeaway

Giving children voice in family proceedings is now widely accepted in principle, but systems differ dramatically in how that voice is heard and weighted. The persistent concern is whether expressed preferences genuinely reflect the child's own perspective or adult influence.

Comparing legal approaches to children's capacity reveals no consensus, only different ways of managing genuine uncertainty. Fixed ages sacrifice accuracy for administrability. Competency tests sacrifice predictability for individualization. Systems that grant medical consent may still override refusal. Voice in proceedings doesn't mean decisive control.

What emerges is that legal capacity for children is not a single status but a collection of context-dependent judgments. A sixteen-year-old might consent to contraception, enter an apprenticeship, but be overridden on refusing a blood transfusion and have their custody preferences merely "considered."

These variations aren't incoherence—they reflect different weightings of protection, autonomy, and administrative practicality across domains where the stakes differ. Any legal system choosing differently has not found the right answer; it has chosen different trade-offs.