This is normally said in exasperation when a child has not jumped into action at the first time of telling. It is often swiftly followed by I won’t tell you again… which may mean either I will tell you again (ad nauseam) or I will give you a slap!
So we expect children to listen to us – and to pick up on the many different ways we say things, together with interpreting the idioms, the hints, the sarcasm, the teasing, the facial expression and tone of voice. And we expect them to know we always talk sense, unless of course we’re talking nonsense on purpose as a game.
Sadly, however, adults often forget to extend the same trust towards children that they are talking sense – from their knowledge and viewpoint. So the adult may say or imply the child is talking rubbish because the adult forgot to extend the courtesy of trying to make sense of the child’s utterance.
1. Adult showing photo of large truck: What’s this?
Child (confidently): Bigwig.
Adult hasn’t seen the right TV show to interpret this as big rig and reacts as if child is talking nonsense.
2. Child: Why bus stopped?
Adult: More people are getting on.
Child: No bus-stop there.
Adult: We can’t see the bus-stop. [It’s too near the side of the double-decker bus to be seen from the top deck.]
Long pause.
Child: Are there clear bus-stops?
Adult (puzzled): What? No. [And does not think the child might have thought that the bus-stop can’t be seen because it’s clear like clear glass!]
If we as adults expect children to be saying something sensible, and take the blame if we don’t understand, then real communication may take place. If we don’t take the trouble to think What could this child be trying to express? then the opportunity will pass by (a) to gain insight into a child’s thought processes, and (b) to demonstrate understanding by making a sensible reply which may include a model of how it could have been said better.
Idioms are fairly confusing for children and foreigners alike! These set phrases can’t be turned around or changed – that is proscribed by our linguistic rules.
Child: I didn’t see the squirrel.
Adult: You didn’t look properly.
Child: I did. I peeled my eyes.
Adult: Oh well. Next time we’ll both keep our eyes peeled and we’ll be sure to see it.
(This helpful adult understood the child had attempted to use an idiom. Instead of saying You’ve got that wrong, the adult used the idiom correctly in her own speech – providing a modelled example.)
If you are involved with a child who tries to communicate but is very hard to follow, try to spend at least some time with pictures or a game where the content is in front of you both! The hardest remarks to understand are likely to occur when the child launches into a stream of talk including names and events you know nothing about. And the child nearly always knows you don’t understand when you make remarks pretending that you do!
languageisheartosay.com 
Beware of germs!
Heard while Covid is still a fear:
In a public convenience a mother saying to her daughter of about 3y, “Don’t touch anything!”
(Good luck with that!)
And near the sea between a father and his son of about 4 or 5y:
Boy, “Can we swim today?”
Dad, “No. They’re discharging raw sewage.”
(Well, I hope not just there by the pier as the first stage in the local ironman triathlon starts with the participants diving off that pier next day for the swimming!)