My daughter’s son has used my credit card to make purchase’s on my credit card with out my authorization I need this to stop now!
How do I stop 🛑 allowing purchasing with my credit card on the iTunes Store????
This is a really wide open question as phrased. You do not provide much background to this such as how old the child is, or if you or he or your daugher are part of Family Sharing and if so, who is the organizer.
One simple solution is to find out who is really doing the wrong thing here and set a password on the device so they cannot make purchases. At the other extreme, this could be considered card fraud and you have the person arrested.
Use a passcode with your iPhone, iPad, or iPod touch - Apple Support - https://support.apple.com/en-us/HT204060