If I don’t have my phone hooked to a service or anything but I have WiFi can I still FaceTime people on it?

The reason why I’m asking is I am about to switch to an android phone and my three year old and his dad FaceTime quite a lot, I would use Skype but those apps never worked that great on any of the android phones I’ve had before so I thought if I could I would use my iPhone for their FaceTime calls.