General help

Moodle 3.10.  Appreciate any help with this - is there any method to Auto Add a user to a specific cohort when the user successfully enrols in a course? 
Scenario is this - it's a school site - parent registers then registers child.  Parent logs in as Child and enrols the child in a course collection. Enrolment is PAID and associated courses are meta-linked.  Courses are split into Year Levels (1 to 6) - for each Year a "main" course, with PAID enrollment - associated courses are hidden and meta-linlinked to the main "Year" course.  Once enrolled, the child (student) is manually assigned to a group (class 1, class 2 etc)  and we use a plugin to update groups through relevant  meta linked courses.  I have one cohort for each "Year" course collection.  Existing students enrolled in each Year, are assigned to respective Year cohorts. 
Next, competency frameworks are set up - one for each meta-linked course.  Then learning plan templates and cohorts as set up previously are assigned to learning plan templates.  Now, learning plans are automatically and correctly generated for each member of the cohorts.  Groups are not changed or affected.  Course competencies also added as relevant.  All above works as expected.
Now, I want to AUTO ADD new enrolments to relevant cohorts.  Is there any way to do this?  Example, new student enrolling in Year 1 to be auto-added to Year 1 cohort.  Does anyone know if this is possible or of a plugin that can do this?
Many thanks
Dave