I have an an older iPhone I want to give to my grand daughter, how do I dis associate it from my number, can I get a new SIM card for it??

I have an older iPhone I want to give to my grand daughter, how do I get a different number associated so that it's not tied to my number. Can I just get a different SIM card?? I don't care if she has all my pictures but everything she does when connected to wifi is associated with my profile. I'm not adding her, I just want her to be able to FaceTime, snapchat, and anything on a WiFi network.