Answer
Only use an age-appropriate licensed product. The adult product is not for children under 12; the children's product is licensed only for ages 6 to 12. Never use it to cause sleepiness.
Sources for this answer
- Benylin Chesty Coughs (Original) — Current selected SmPCemc · Summary of Product Characteristics
- Benylin Children's Night Coughs — Current selected SmPCemc · Summary of Product Characteristics