One of the most exciting aspects of being a parent or caregiver is coming to know your child – understanding their personality. Infant temperament can be thought of as an early indicator of personality. While there is some stability in temperament across time, it is important to note it is not deterministic. We are always changing as individuals. An understanding of an infant’s temperament is a fun, exciting way to think about your child’s development. Scientists think of temperament as individual differences in emotional regulation and emotional reactivity. Parents and caregivers think of it as “who” their baby is – likes, preferences, and flexibility of their burgeoning being.
In the late ‘60s and ‘70s, researchers spent hours asking parents about their infants. Boiling down these interviews, research categorized babies in 3 groups, which have been pretty well replicated in future work, and tend to get head-nod approval of most parents reading the descriptions.
Type 1: Easy babies: These babies are generally happy, easy to calm when upset, and are flexible in new situations. Generally, easy babies tend to quickly establish a day/night routine. This doesn’t mean that easy babies don’t cry – it just means that when they are upset, a few patented parenting moves (swaddling, bounding, holding, making the “shush” noise) work most of the time and they tend to work pretty quickly. These babies can be at home or brought into a busy place and are generally not overwhelmed. This doesn’t mean that these babies don’t have bad days or get overwhelmed, but that most of the time, babies in this category are pretty easy.
Type 2: Difficult babies: These babies have a more difficult time adjusting to new situations or schedules and tend to react loudly and negatively to new situations or events. Soothing these babies is also a bit more difficult. Difficult babies are the babies that a trip to the grocery store is only possible under perfect conditions (just fed, favorite snacks packed, special blanket, well-napped, and recent poop). When upset, it requires a bit more ingenuity to soothe these babies (think: cardiovascularly intense caregiver squat jumps). Certainly, these babies smile and laugh and are loving towards their caregivers, they are just a little bit more reactive than easy babies.
Type 3: Slow-to-warm-up babies: These babies basically start out as difficult babies and transition over time to easy babies. After being exposed to new people and places, these babies adapt and react less strongly to new situations and people. They might always be a bit more skeptical of new situations or more reactive emotionally, but they can generally adapt to their surroundings.
Before you get all caught up into these categories, know that generally 40% of babies are categorized as easy, 10% as difficult, and 15% as slow-to-warm-up. That leaves a whopping 35% of babies who don’t fit into these categories. Because of this, researchers broadened their ideas of how to think about infant temperament.
More contemporary work on temperament looks at six different features of infant temperament: fearful distress/inhibition, irritable distress, attention span and persistence, activity level, and positive affect/approach.  This approach is how scientists today think about infant temperament.
This cluster of temperament traits is a bit like an adult personality test – for babies! Fearful distress is how much an infant is distressed by new situations (Does your child cry or show distress at loud noises?). Irritable distress is fussiness, anger, and frustration, especially if an infant doesn’t get what he or she wants (When having to wait for food does your child seem not bothered, fuss, or cry loudly?). Attention span is how long or often an infant is interested in looking at something (Does your child play with an object or toy for ten minutes or longer?). Activity level is how much your infant moves (While eating, does your child lie quietly, squirm or kick, or wave his or her arms?). Positive affect is basically how much your baby smiles and laughs and how willing he or she is to approach new people (When tossed around playfully does your baby smile or laugh?).
By thinking about your infant’s reactions and emotions, you can get a sense for where they fall on each of these scales. Of course, it’s important to think about your child’s temperament on average. In my family, # 2 had terrible reflux and cried 32 hours a day (ok, it felt like that) for the first 6 weeks of life. After some treatment for reflux, it was a whole different baby. Had I measured # 2’s temperament for the first 6 weeks of life, I would have created a new scientific category: demon baby. But after the tummy troubles passed, I got a chance to know # 2 – turns out, that one was a pretty cool baby.
With a basic understanding of temperament, the question for a parent or caregiver is, why do I care? Well, temperament is interesting for two reasons. First, it is interesting to know how your kid got their temperaments. Second, it is important to understand what temperament means for how your child interacts with the world.
First, how to children end up with these temperaments? Of course, there is a strong genetic basis for these individual differences in infants (already, you can blame mom and dad for something baby!).  But, like all aspects of human development, genes are not the entire story. Environment and early experiences can affect behavior and temperament. For example, exposure to drugs during pregnancy  or high levels of maternal stress and anxiety  can affect an infant’s ability to regulate attention and behavior. After birth, high levels of stress or abuse can affect a child’s temperament as well. Thus, while temperament is influenced by genetics, environment plays an important role in how this genetic predisposition will be expressed. Furthermore, because of this complex interplay between environment and genes, temperament is not completely stable. We are always changing as people, and the same is true for our infants and children.
Second, temperament is important because it helps us understand our infants. If we recognize that our infant has some challenges when in a new environment, we can think about ways to help them succeed in that environment (for instance, going to the grocery store at 6 a.m. when a baby is recently fed and had their longest sleep). It also is helpful for us as parents and caregivers going forward. For instance, as an infant, # 1 was very high in attention. This is a trait that is still a core feature of who #1 is. For instance, at the age of 4, # 1, could sit through an entire soccer or football game perfectly rapt with attention. To me, as a nerd, this is just a continuation of the 3-month-old baby that intensely studied a Christmas tree for 40 minutes straight. Observing and understanding temperament is an interesting indicator of the children and teens our infants will become.
 Rothbart, M. K., & Bates, J. E. (2006).
 Rothbart and Bates have a sixth category of infant temperament, rhythmicity, but this category is not used in measurement of temperaments and not discussed here.
 Rothbart, M. K., & Bates, J. E. (1998).
 Dennis, T., Bendersky, M., Ramsay, D., & Lewis, M. (2006).
 Huizink, A. C. (2012).