It is a legal requirement in England for children to attend school from the age of 5 until they reach school leaving age. Government guidance explains the dates when a child becomes of compulsory school age and when they reach school leaving age.
All children can receive free education at a primary or secondary state-funded school from the age of 4 to 16 years old, continuing to age 18 if they are attending sixth-form.
State-funded education is not classed as a public fund for immigration purposes and can be accessed by a child regardless of their immigration status.
The only children that are not able to access state-funded education are those that have leave to enter or remain as a visitor, Tier 4 (Child), or short-term student (child), due to a study restriction.
See the government information about school admissions.