Then how do your kids communicate with those who only have android devices? That's a big social issue among teens in the US.
iMessage is never popular in Europe, as everyone here uses cross platform apps like Whatsapp, Telegram, Snapchat, etc. due to the lower market share of IOS vs Andorid.
Some of the auto updated apps have a history of adding circumventable embedded browsers in about boxes and things on Android which can be used to browse the internet. This happens on iOS too but the browser engine is safari and is subject to the same white lists as normal Safari.
This is a fairly large security concern if I'm honest generally.
Teach them it's a tool and guide them on how to use it responsibly.