Grant automatic guardianship to parents of 18yr olds who lack mental capacity

For those who've had parental responsibility for a child and advocated for the child's wellbeing and health throughout their life, I want them to be able to continue guardianship of their adult child automatically without having to apply for it.

I'd like this to apply only to parents who've been actively involved in supporting their child's health and wellbeing throughout their life. I think they should automatically be granted continued guardianship where their child lacks mental capacity.