I certainly use WhatsApp and like what Burgo said, some use it beautifully but to others it's a mystery.Some parents just won’t do it though.
In my team about 1/4 of the parents won’t use the group. Some a great communicators but prefer to contact me directly.
This was the same at my old team. Different club, different parents, similar situation. 75% use the group/app, about 15% prefer not to use the group comms but are still good, and about 10% just don’t communicate at all.
I had to call out two parents this year. Basically told them that if they can't be bothered bring their kid to training and communicating with the coach, all bets are off as to whether or not they ever go on the field. This was extreme though. These kids were at 5-6 training sessions each over a period of 3 months.
In Burgo's post above where I've highlighted, I find that those who won't use the group also don't communicate with me directly. I always have to chase them. I also get incensed when I have sent a message out with information and someone comes on and asks a question on something I have already communicated. Like, for example, I'll send out the details of where we are playing and what time, and some idiot later that day will come on and ask "So, where are we playing on Saturday? And what time?" My blood absolutely boils at that.