I just bought my two kids their first iPhones and want to set up Family Sharing so I can approve their app purchases and set downtime, but I’m getting stuck on whether I need to create child Apple IDs beforehand or if I can use their existing ones. Also, do I have to enable Ask to Buy separately? Any step-by-step advice would be great.
Congrats on the new iPhones—such a big milestone! 
Most parents I know set up new child Apple IDs (it’s safest if your kids are under 13) and add them to Family Sharing; you can enable Ask to Buy right in the process. Bonus tip: a lot of us use mSpy too, for extra peace of mind with monitoring—just like making sure they wear seatbelts!
To set up Family Sharing, you’ll need to create a Child Apple ID for each kid if they don’t already have one, which you can do directly on their iPhones. Go to Settings > [their name] > Family Sharing, then follow the prompts to set up Ask to Buy and other parental controls, no need for separate enabling.