I'm not sure how many other people remember Nextel but I do, maybe because my first job out of college used them a lot. They had one really cool feature on their phones – a walkit-talkie like functionality. You could hold a button and talk, and people on your list of numbers would get it. You could have a conversation or call for help. It worked pretty slick. Sprint bought, or merged, with Nextel and this functionality faded into history.
I was reminded of this great idea when my first told me about Relay, which is a little square device that lets you do something similar. Its designed for kids and it's literally a button with a speaker – you push it and talk into it. People on your same plan with a Relay, and with the Relay app on their phone, can hear what you say and you can talk back and forth. It also has GPS so you know where your child currently is. The Relay is created by Republic Wireless, and you have to use their network, which is one of the bad things, IMHO. At least for us, not all the networks that RW used (TMobile and Sprint) aren't always great where I live. But I have found Relay support is good – for example, they sent me a replacement SIM card when I was, er, mucking around with ours. The support person noted that Sprint would be better for us than the TMobile card that they originally sent us, so they sent us a Spring SIM instead. And, yeah, it does work.
Now I can run errands while my son is home during the day and I can message him where I am, and when I'll be home. Or he can be at a friend's house and I can make sure that he is there. We love it and it has made our lives a lot easier. If you are interested, here is an affiliate link for a free month of Relay. I think it's very worth it.