IDE: Spring Tool Suite 4  

Framework: Spring Boot  

Gradle: v6 

I have created a multi-project gradle build consisting of 3 child projects A, B and C. I want to create a custom task in the root build.gradle to achieve the following
Running the custom task will  

1) Execute the child project A's bootRun task.  

2) Then after few seconds, execute child Project B and C's bootRun task 

\*bootRun is a task that run the project as spring boot application 

Note that child project A is a server, so it will keep running in the background, whereas child project B and C are the client to the project A (server). 

Question is how to write such custom task to achieve the above?