Almost 80% of the children treated were girls.
Nearly 1,100 children were treated in hospital for drug or alcohol-related issues last year.
According to freedom of information figures, 79% of these children were girls.
The new figures show the total was 4,245 last year for the number of people who were treated in hospital for drug and alcohol-related issues, with one quarter being children.
Some 1,070 under-18s were treated for these conditions, an increase from 914 in 2020.
733 young adults, aged between 18 and 25, were treated in hospital for these conditions last year.
These figures relate to inpatient and day-case admissions only, for conditions like intoxication and drug-poisoning.