Four-year-olds are among hundreds of children being referred to specialist drug and alcohol treatment services, it has been revealed.
After being approached under Freedom of Information laws, councils across England, Wales, Scotland and Northern Ireland gave the ages of children who were referred, which revealed four-year-olds had been referred in South Ayrshire.
Eight-year-olds had been referred to services in Waltham Forest and East Ayrshire, while nine-year-olds had been referred in Herefordshire, Liverpool, Oxfordshire, Rutland, the Scottish Borders and West Berkshire. Five other authorities had 10-year-olds referred.
Keith Vaz, chairman of the Home Affairs Select Committee, said: "I am deeply concerned that children so young are clearly gaining access to harmful substances.
"It is right that these youngsters receive the appropriate help but we must look at the source of their problems.
"It is vital that parents take responsibility and additional support is given to them in order to prevent children being exposed to drugs and alcohol in the first place."
A referral can mean the child is vulnerable to drug and alcohol misuse through exposure from a relative, or could have started abusing substances themselves.
"Families hide things," Scott Haines, family development manager at drug and alcohol charity Addation, said.
"Family issues can be a big part of why you develop substance misuse in the first place but also quite an effective part of the solution."
He added: "If there is a particular incident - we have to find out if it is isolated, is it a pattern in behaviour? What has influenced or shaped that behaviour, is a young person hanging around with older youths who might be influencing them in some ways? Is there an adult, are they getting it from the home? Are parents not keeping an eye on what's going in or out?"
Andrew Brown, from charity Mentor UK that works to protect children from drug and alcohol misuse, said he was shocked at the findings.
He said: "We think it is vital that alcohol and drug education improve. Our own survey of teachers suggests that at the moment delivery is inconsistent, and that the norm is to timetable only one or two sessions a year."
More than half of under-13s referred - 59% - received treatment for cannabis misuse, while a third were treated for alcohol misuse.
Children are most commonly referred for treatment by education providers or youth offending teams.
Schools are required to teach the effects of drugs on behaviour and health as part of the national curriculum.
A new national curriculum being introduced in September says pupils in Year Six - those aged 10 and 11 - must be taught to "recognise the impact of diet, exercise and drugs and lifestyle on the way their bodies function".
Although PSHE lessons remain non-compulsory, the Department for Education recommends schools use them to expand the knowledge pupils get in science classes.
A spokesman said: "Teachers are free to use their professional judgment to address any specific issues that meet the needs of their pupils through PSHE. We are working with the PSHE Association to help teachers talk about these issues with pupils in the most effective and sensitive way."