I usually in answering a question don't pry but are your kids teens and a reason you found it needed to do this? That can I am sure you know be pretty bad between kids and parents. Having said that I can't think of anything to tell you other than to give you this link as a start from the Apple website that might give you a start on what you might be able to do and also give you time to think about all thins. Good luck in what you decide.
Apple - Support - Search
EDIT:
Let me ask you this since I reread your question.... Are you trying to change the number for the iPad that he is using meaning is the iPad a WIFI and cellular usage with a phone number? Do you want to change it to your number so you receive the texts assuming you are using an IOS device? That i can tell you but i would like to hope someone else sees this and chimes in on what they think. I might contact someone to look in on this post.