If someone stays in UK for 7 years with a Child and spouse, then can he get PR based on his Child’s continuous residency for 7 years?
If you have a child who has lived for 7 years in the UK will be eligible but keep in mind it’s only the child’s application that will be considered. Not the parents.
Secondly, there’s also another very important point people often ignore when considering this route. UKVI clearly says that they will only grant leave to the child IF it is not reasonable for the child to leave the UK.
So, when considering this route, you’ll have to shows several proofs of evidence to prove home office that the child (and parents) have made strong ties in the country. Now that will depend on how you prove it. Maintain proper documentation of the entire 7 years. Documents such as nursery, school reports, medical documents, reference letters from friends/community leaders who have known the family for 7 years, etc.
The home office can never separate the child but what they can do is refuse both the child and parents if they decide not to give a visa to the parents.