Hello Renaenae67,
Thank you for posting to Apple Support Communities.
We understand you'd like to share you purchases. Apple has a good support article on how to set this up. Take a look: How to share purchases with your family - Apple Support
To share purchases, you'll need to allow your method of payment. However, you can turn on Ask to Buy for the child's account. That way, charges will not go through automatically. Enabling Ask to Buy can limit children from downloading free apps as well. You'd be in control. You'll be prompted and can deny or allow them: Approve what kids buy with Ask to Buy - Apple Support
That should help. Let us know if you have any questions.
Take care.