Thanks for various comments re WhatsApp and especially for the reassurance that BA try something else if message not delivered.

I perhaps should have said that I choose not to use WhatsApp. I was on the verge of signing up when it was acquired by Facebook and, as I will have nothing to do with them, I carried on without it. Life goes on with text messages, emails and sometimes I even talk to people
My children don't seem to find it a problem and I have resisted the muted encouragement from my wider circle of friends and family. I'm certainly not signing up for BA!

I do understand what it is and why people find it incredibly useful.