This is a useful transition from that IME - when they are in a tricky age like 4/5 where they want to interrupt and know that they should wait, but they struggle waiting for too long. Once they're say 7 or 8, they should have transitioned to more of a reading the room and interrupting only at a reasonable moment.
It's like putting your hand up at primary school - it is a helpful signal to the child realising that "I have signalled my intent to speak, and the teacher is aware" and helps them remember to stay quiet until it is their turn. But my 5yo (possibly ND, and not at school yet - abroad) finds this really really difficult, if we just tell him to wait, about half of the time he will start jiggling around as though he has ants in his pants and about half of those times he'll burst into tears and say "But I'm going to forget!" The jiggling/upset is more likely if he's tired, hungry, or if we ask him to wait longer.
If you want to train a skill in children like waiting for an appropriate pause in the conversation, it really helps if you can start with an interval that is easy for them such as getting them to wait around 1 minute, and then increase this over time until they are able to wait several minutes. You should not always respond to DC until the day they turn 3 and then just suddenly expect them to sit there patiently for 10 minutes - which feels like an AGE when you're waiting for something - you have to build it up from a reasonable expectation. If they are a child for whom this is especially hard perhaps due to lower impulse control, then start with an even smaller interval like 20 seconds.
This is not totally child specific psychology either - adults will get frustrated after a very short time if they do not have an indication that someone is aware that they are waiting. It's just that most adults have developed an understanding of conversation cues so we can read whether someone is aware and will get to you, or isn't listening at all. That's why telephone call centres use hold music and/or tell you what position you are in the queue, because if you are just on the phone listening to silence or static on the line, it's really not clear if someone will answer your call or they have just hung up on you, and many people will hang up.
Children won't have that awareness when they are very young so being able to put their hand on your arm, or put their hand up in class, is a useful short cut for them to bridge that gap while they develop the skill.