While babies can't understand the complexity of a situation, they can tell the difference between a parent who is happy and one who is sad. Research shows that even infants as young as 4 months are able to distinguish different emotions in adults. In one study, researchers used the game of peekaboo to act out anger, fear, and sadness for babies, and found that they reacted differently to each one. For example, infants paid more attention in response to anger and avoided looking when sadness was conveyed.
That's not to say that every time you and your husband snap at each other in front of your baby you're doing psychological harm. These occasional events are normal, and can actually teach your baby about conflict resolution. However, since babies lack coping skills to deal with stress and sadness, they may react more viscerally to serious or regular squabbles and become cranky and unsettled or have trouble sleeping. If you feel a big blow-out with your husband coming on, let your anger simmer until you have some private time to talk things through, like when your baby's sleeping.
Originally published in the December/January 2004 issue of Child magazine. Updated 2009.