Children learn by observation, probably better than adults. When children witness parents criticizing each other, other people, or the child, then they grow up believing that the standard for how to live in the home is critical in nature.
The result often leaves an atmosphere of competition, striving to be better than someone else in order to avoid being criticized.
To prevent this from developing, we need to stop and think before we speak. We may need to apologize to our children for how we have criticized them or others in the past. Above all, we must strive to set a more positive tone for the future.