Set up Google Play for restricted user accounts
Follow Following steps:-


First you have to make a gmail id for your kid.
Then open clash of clans and in settings use connect to supercell id follow this video https://m.youtube.com/watch?v=D7zX0kETazA] 
After connecting your kid account is connected to supercell id means id is backup online.
Now uninstall clash of clans from admin account and open your kid account and download again in that account from play store.
After install in his account just reconnect to supercell id by using newly created gmail.
They will send sign in code on Gmail open gmail app and account in which you have backup his account copy that code and enter in game.
Now all done nothing is connected to your admin account and clash of clans has ended support to Google play games. 


But Still If you want to connect to Google play use following steps:-


Create a new Gmail id then.
Open clash of clans and go to settings double click on Google play button.
An menu will pop up which shows you all accounts that you have in your device.
Just select newly created gmail which is created for kid all is done.
Uninstall clash of clans and logout admin account.
Open kid account download again From store and reconnect to Google play by double tapping on Google play in game settings and select newly created gmail account.


He will got his progress back any questions are most welcome.