In an article for Men’s Health, Sandra Nygaard mentions four surprising things toddlers understand.

1. Lying “When an adult’s emotional message differs from the verbal one, even 1-year-olds notice,” says Joan Klinkner, an early-childhood education instructor and the coauthor of Social & Emotional Development.

2. Fighting “Young children may not understand specifics, but they can definitely sense when something isn’t right between Mom and Dad,” says Tim Seldin, president of the Montessori Foundation and the author of How to Raise an Amazing Child. Wrinkled faces, secretive conversations, and tense tones are the dead giveaways to children less than a year old. Just be honest early and often, says Klinkner: “Mommy and Daddy are having a disagreement right now, but we’re not mad at you. We love you.”

3. Bad Words Children as young as 18 months pay attention to inflections or emotions attached to language, says Carolyn Edwards, a professor of psychology at the University of Nebraska at Lincoln. These words are mysterious and powerful, which is why kids often repeat them. “If your child says a bad word, respond matter-of-factly,” says Klinkner. “If he gets a big reaction, he’ll continue to use the word to feel powerful.”

4. Gender Roles At age 2, children notice what moms and dads generally do. By 4 they’ve accumulated a set of gender expectations. “By grade school, they strongly believe those stereotypes,” says Edwards. Your play: Mix up your roles at home by, for example, taking turns cooking dinner.