Sorry, I’m unclear what you wish to do. Are you saying that you want to transfer your son’s Telus prepaid account to a monthly Koodo postpaid account?

Right now the account is under me and  my sons wants to get his own account but have the number I have. As it was his phone  just under my account 

So he wants his own account with another provider but keep his number? That's actually very simple.  Have him sign up with the service he wants.  Once that is done, he can port the number across. 

But the number is under my account not his but I want him to take the number 

Right, so if you have an account with two lines (yours and his), once he transfers his number to his new account, it will automatically close that line in your account. Then all that's left with Koodo is your own line.