I am not tech savvy at all, and with my recent research I am coming up empty handed looking for a specific app.

So my question is;
Is there an app that you don’t need a phone number and we can use between my Apple iPhone, and my children’s at-home Android phone, that only uses a WiFi connection? More specifically, I am gone from the house and can still reach the older kids on their Android that has WiFi only?
Now I know those apps exist but I am looking for one that is more private and doesn’t track like FB Messenger. So far all the ones I found either track you, need a number to function, or outside people can contact and solicit you.

Is there anything out there like this that has worked for you?

Signal is supposed to be a pretty good app for privacy. I use it

I am trying to save money by using an old smartphone and an app with WiFi. It is more expensive having a cell phone or a landline hooked up to a number when we already pay for WiFi here at home. The smartphone has all apps with internet access removed it is only for texting and calling, once we find the safest non-tracking app.

I've heard of Signal and Wire. I believe neither of these apps require your phone number and are more privacy oriented.