There are two ways to create a child project;

1. The most common way is to create an entirely separate solution/project for each adapter. When you have this (child) solution opened, you'll only see the child project and perhaps a parent project of this child used to test it. Once you've finished its development, you would then open your parent project. From here, you would simply right-click on your solution in the Solution Explorer window and select "Add Existing Project". Browse for the child's "osproj" file and click "Ok" to add it to your solution. Next, proceed to the last paragraph.
2. A less common way is to create a child project directly within the parent solution. To do this, right-click on the solution in the Solution Explorer window and select "Add New Project". Once you name it and click "Ok", the project will appear in your solution. Next, proceed to the last paragraph.

Once you have a new project in your solution you must reference it. To do this, right-click on the References folder and select "Add Reference". Select the "Projects" tab and select the project(s) you wish to reference. After adding a reference, you must then import the projects into the main project. Right-click on the parent project in the Solution Explorer window and select "Manage Imported Projects". Move any projects from the "Available Projects" box on the left to the "Imports" box on the right by clicking the arrows. Now, when you click "Run", all of the projects will start.

You need to have a common interaction.xml once you added to a single solution. 

Thank You Thomas for your inputs, I have imported all the child projects and added references as well, but system executes only the parent project. Could you please help me on this?

Appreciate if you share any demo video. 

Thanks in advance!