If your child does not learn from you now that it is okay to say no, then when and from whom will they learn that?
What happens when your child says “no” to you? What happens to your eye contact, your facial expression? Consider that the word “no” is both one of the most reactive words a parent can hear from their child, yet is also the one word we parents really want our children to be able to say to others when they are older. So much of our early experience of the word “no” becomes associated with a sense that saying “no” is bad or wrong, or at least not nice - even though we know it might be more honest.
What can a parent or teacher do about that? You can show your children that it is okay to say “no” by making a lot of requests of them, to help out or do things, such as put away toys, get dressed, eat their broccoli, but be sure to include some are optional, and that are not health or safety issues. Examples of these are: will you bring me a tissue, or a diaper, or put this napkin on the table, or find my phone. When you get a “no,” you can even say “okay ... that's fine” with a smile of appreciation. Help “no” be a useful tool, a helpful word for your child.