Texting/calling app suggestions

I habe two bonus kids a boy and girl boys older and has a phone on our plan. We recently found out our daughter was upset her brother has a phone and she doesnt, so I was gonna let her have her brothers old phone just to use on WiFi and download a texting/calling app for her to use but I cant find one kid friendly so if anyone has suggestions I'm open to it. Also would like to add I have a monitoring app on it as well she cant download anything with out my permission it asks for a password and everything,