Four cases involving children and their families and two additional cases involving only children were analyzed in this study.

Children spend a significant amount of time in close proximity to their parents within the home environment and are particularly vulnerable to environmental exposure. As mobility develops, exploratory behavior, such as touching surfaces and placing objects in their mouths, increases the risk of contact with contaminated substances. Furthermore, hair characteristics differ between children and adults and may influence the incorporation and retention of toxic substances depending on age and the sampling period. Several studies have demonstrated that children's hair is typically thinner and more porous than adult hair, facilitating both external incorporation of substances and potentially enhanced elimination through washing practices such as shampooing [17, 18, 19]. This latter characteristic may partly explain the absence of certain molecules, such as methadone or other psychoactive drugs, in our pediatric cases, in contrast to numerous reports in the literature [17].

In this series, cocaine and its metabolite BZE, together with THC, were the main substances detected in cases of child exposure, in agreement with previous studies [20, 21]. Accidental cocaine intoxication in young children has been widely reported and is typically associated with symptoms such as tachycardia, seizures, agitation, and altered consciousness [8, 22, 23, 24]. Although Arbouche et al. [21] reported drowsiness as the most frequent symptom in pediatric cannabis intoxications, this was not observed in our cohort, even in cases with positive results in other biological matrices. The absence of a clear correlation between toxicological results and clinical symptoms in our study supports environmental exposure rather than acute accidental poisoning. This observation is consistent with a 2023 Italian study [8] reporting no statistically significant association between substance concentrations and clinical manifestations, suggesting that exposure levels may not directly predict clinical severity. In addition, the potential for missing or incomplete data must be considered. Case 2.1 is particularly noteworthy, as the simultaneous detection of cocaine and BZE in hair, urine, and blood strongly suggested active exposure (Table 3). The concentration ratio between the first two proximal segments was close to 1:2, and concentrations measured in the child were approximately tenfold higher than those observed in the aunt. Overall, cocaine and THC concentrations tended to be higher in younger children, with ratios ranging from 10 to 100 compared with adults, a finding consistent with previous reports and likely related to age‐dependent hair characteristics [25].

Substance concentrations in the suspected adult consumers generally exceeded the cut‐off values for drugs of abuse proposed by the 2021 Santiago consensus of the Society of Hair Testing (SoHT) [12], with the exception of the father in Case 4.4 (Table 3). It should be noted that these cut‐offs are validated for head hair only [11]. Axillary hair is not the best alternative because of potential wash‐out effect from sweat, differences in drug incorporation mechanisms, and generally lower concentrations reported for many compounds [26]. Nevertheless, axillary hair analysis, together with other keratinized matrices such as nails when head hair is unavailable [27, 28], remains valuable for qualitative assessment. Moreover, analysis of all household members, including fathers who may be less accessible as highlighted in previous studies [25], is essential for accurately documenting each family member's exposure or consumption histories.

THC‐COOH, a metabolite indicative of active THC use, was not detected in the hair of any suspected adult users in these cases and was found in the urine of only one mother. In contrast, THC‐COOH was detected in both blood and hair in Case 6 (Table 3), suggesting very recent intentional consumption by the child shortly before sample collection. These findings may also be related to the relatively high LLOQ (1 pg/mg), whereas the minimum required LOQ for THC‐COOH confirmation is 0.2 pg/mg [12].

These cases highlight the difficulties in determining the precise source of drug exposure in children. Potential pathways include in‐utero transfer, postnatal exposure through breastfeeding, environmental contamination via inhalation or ingestion (accidental or intentional, such as in Munchausen syndrome by proxy), and external deposition onto hair from passive smoke, dust, contaminated surfaces, or parental sebum and sweat [5, 6, 29, 30, 31, 32]. This complexity is further compounded by the difficulty in distinguishing acute from chronic exposure in pediatric populations, an issue emphasized by Alvarez et al., who recommend caution in the interpretation of results, particularly in children younger than three years [33].