I set up a my child's apple account; in family share but how do I assign his Ipad to him? it is currently set up under my user name/account

Start by completely scrubbing your own info off the device, and then scrub the device from your own AppleID.

What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support

Then, completely set it up “new” as his.

Set up your iPhone, iPad, or iPod touch - Apple Support

Good question.

Since he was sharing YOUR AppleID, the Apps are actually yours.

Once you have it all up and running, most apps will allow you to share them w/ family members.

There may be some data loss depending on how any game or app keeps track of users/players, but the long-term benefit of having separate AppleIDs will FAR outweigh any short-term “problems” encountered.