A child’s invented word can describe something the household never named before.

Children invent words because they need one and the language has not supplied it. What they come up with often points at something real that the household had been experiencing without a name: a particular kind of tiredness, a specific noise the boiler makes, the feeling of the last day of a holiday. Once the word exists, everyone can see the thing.

Keep the good ones and use them properly rather than as a joke about the child. Write a few down somewhere, with dates. Families that hold on to their own vocabulary end up with a shorthand nobody else can borrow.