how to create an apple id for your child

You can create an id without accredit card that might be what you want. Ten use that ID for your child's iMessage and iCloud and use your ID for iTunes and App Store on both phones. That way you can control what is purchased. I would set up restrictions on the kid's phone with a pun that you only know and durn off in app purchases

Set up an account for yourself on your child's behalf, and create an "allowance" to use for purchases.

How to set up an iTunes Allowance

What do you mean by "Set up an account for yourself on your child's behalf"?