Background When children aged 0–4 years are analysed together as a group for poisoning risk, important differences for smaller age intervals by medicinal and non‐medicinal substances are masked. These differences have been attributed to child developmental stages but no studies have been conducted that examine the predictive value of child developmental stage for poisoning by substance type, using 3‐month age intervals as a proxy for developmental stage and adjusting for the effect of sex, socio‐economic status and remoteness of residence. Methods A population‐based dataset of unintentional poisoning hospitalizations in children aged 0–4 years was used to predict the type of substance ingested. Associations between the type of substance and age, sex, socio‐economic status and remoteness of residence were measured using multivariate logistic regression. Results Children aged 12–17 months had significantly higher odds of experiencing a non‐medicinal poisoning while children aged 24–41 months had significantly higher odds of experiencing a medicinal poisoning. Males and children from more disadvantaged and outer regional areas had higher odds of experiencing a non‐medicinal poisoning. Conclusions Children aged 0–4 years differ in their stage of development and as a consequence, vary significantly in their ability to access their environment. Our results clearly show that odds of poisoning by medicinal substances compared with non‐medicinal substances change as children age. This study provides evidence that child development predicts the type of substance accessed and ingested.