Why do I get messages saying my AppleID is being used to sign in on my daughters I pad

Remove your Apple ID from the iPad if its being used there.

You are getting the message, because ostensibly your Apple ID is being used on the iPad for something.

See here for all the places an Apple ID can be signed in on an iOS device: Sign in with your Apple ID - Apple Support

Change your password.

 Apple ID Password Change

 What to do after you change your Apple ID or password - Apple Support     I suggest doing this before you change your Apple ID or password.