My kids, now teens, had a set of walkie talkies. It's really CB radio talk.
The first speaker says "Come in" and ends with "over".
The word "over" lets the other person know you're taking your finger off the button and will be able to hear them. Every section of conversation must be followed by "over" and removing a finger from the "talk" button. You can not hear the other side while you hold the button. Kids never remember to release the button or signal that they've done so.
If someone says over and out, they are both passing the conversation from themselves and leaving. As in I'm out of here.
As to whether kids still do this today, maybe check for toy talkies in the store. CBs still have applications IRL. Police and truck drivers still use them as far as I know, so kids are likely to. This is especially true if they watch cop TV or Paw Patrol.