Don’t simplify your language in front of your children. Their little minds are capable of grasping and retaining more information at this stage of their lives than at any other, so make the most of it! Don’t use baby-talk, use the vocabulary you would ordinarily use, but stop to provide synonyms occasionally if you throw out a difficult word.
For instance, tell your child that something is ‘non-negotiable,’ but follow it by giving a definition that she will understand. In order for your kids to constantly be challenged, your vocabulary must be above theirs. You’ll be pleasantly surprised when your three-year-old reports that she wants to, “discuss the issue.”