If a child has been in the U.K. for more than 7 years then the child itself and his or her parents can apply for the U.K. visa. The 7 year child Parent Route can get the people limited leave to remain in the U.K. visa for the child itself or the parents of that child as well.
But here are a few major requirements in order to get the child visa for UK through the 7 year child Parent Route:
1. The child must of the 18 or more years in age on the date of application. Otherwise, the application will be rejected straightforwardly.
2. The child must be living in the U.K. for at least 7 years.
3. If the child is currently living in the U.K. then also a child and his parents can get a child visa for UK.
4. The child has no future intentions to leave the U.K.