Learning the language.
My four year old grandaughter went to a recreation ground/park where she hasn't been for several months and was fascinated to see it had been upgraded.
"Look, Mummy, it's been maintenanced."
"Maintenanced?"
"Yes. That means the old stuff has been taken away and either mended or replaced with new equipment."
My daughter told her the word was 'maintained' but was delighted with the explanation.
This is what happens when you talk to children with real words and don't get stuck in baby talk. Also when you explain things to them as you go along, and when they ask, even if you think they probably don't fully understand what you're saying. Some of it nearly always sinks in.
The little lass loves to explain things to us. Usually prefaced with "Did you know..."