Your baby will begin to understand the meaning of "No" between eight and 10 months. When your baby gets too close to something dangerous, your dramatic response-- "No", plus an alarmed or strongly disapproving tone and expression--will alert her to the fact that you mean business.
Don't Overuse No
Save a strong "No!" for really important situations--like teaching your baby to stay away from danger. You want her to learn that she shouldn't pull the books off the shelf or shred the newspaper, but these are less crucial lessons. The more you use the negative, the less effective it will be. In addition, a frequent "No" sends a disapproving message to your child about her natural desire to explore and experiment.
If you find yourself saying "No" often, try to make changes in your home so your baby doesn't face as many untouchable objects or dangerous situations. Use distraction--it's a creative way of controlling your baby's actions. If she's reaching for her brother's robot, direct her attention to the blocks on the other side of the room. That way you change the behavior without overusing "No".
Provide More Information
Add to your baby's understanding of why she shouldn't do something by giving more information when setting limits. Add the danger words that apply: No! That's hot! It burns! or No! Sharp! Sooner or later, your child will put these clues together. She'll get the idea that the really dangerous situations must be avoided.
What Your Child Knows
Once your child understands the rules about things she's not supposed to touch, she may purposely go after them just to get your attention. You can tell if she knows the difference between right and wrong (Yes and No) from her expression. If she looks gleeful as she heads toward the flowerpot and grabs a handful of dirt, she knows she's misbehaving. If she looks ashamed when you catch her with her sister's toy, she knows she broke the rule.
Toward the end of the first year, your baby will try out her own version of no. She may use it even when she means yes, because she knows it's so powerful.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.