We have used them at DLR many times. With four kids it is not unusual to have us breaking up into 2 or even 3 groups. With walkie talkies everyone can listen in on the conversation. This was 5-10 years ago.
With the growth of cell phones it is just easier to use them now. However, when I went to Tokyo DL I took the same walkie talkies because it was very expensive for us to use cell phones there. Since it was only me and DS13 and we were always together, the walkie talkies were more for emergencies if we got separated.