Learning about illness is unlike learning about other things: it requires children to reason about objects like “germs” that they can’t see or touch.
Although children have some difficulty of grasping the concept of illness and how illness is transmitted, children begin to learn about it in the preschool years.
At first, they acquire very basic knowledge about illness transmission, and can provide accurate explanations for how someone might have gotten sick.
For example, when researchers asked a group of preschool-aged children how another child might have become sick after a sequence of events, even three year olds were able to list accurate explanations for contracting the illness, spontaneously citing germs or contact with a bodily fluid.
But preschoolers’ knowledge isn’t quite complete and they still make mistakes.
For example, the same three year olds had trouble making predictions about who would get sick a day later based on whether they engaged in a risk behavior like eating a contaminated food.
Other studies have shown that five year olds have trouble differentiating between various illnesses, and think that non-contagious illnesses like cancer and mental illnesses like depression are as contagious as the common cold.
It isn’t until a few years later that children acquire a more sophisticated understanding of illness transmission and can make predictions about how engaging in risky behaviours might make someone sick, and differentiate between illnesses that are contagious and illnesses that are not.
How children behave when faced with contamination
Children’s behavior seems to lag a bit behind their verbal understanding of illness transmission, and preschoolers are generally happy to engage with objects — even foods — that have been contaminated.
In one study, researchers presented three- to 12-year-old children with a glass of apple juice and systematically put various objects into the juice. They later asked the children if they wanted to take a drink. It wasn’t until age six that most children rejected the juice when a dead grasshopper was visibly floating inside, and even then, some of the older children still drank it.
Similarly, another study showed that after watching a video of two actors eating applesauce out of two bowls, two- and four-year-old children ate applesauce from both, including one that had been sneezed in by one of the actors.
It was not until ages five to eight that children ate more applesauce from the clean bowl than from the contaminated bowl; and even then, most of them still ate some of applesauce from the bowl that was sneezed in.
Teaching children to stay healthy
Most preschool-aged children don’t necessarily understand illness transmission and how to actively take steps to avoid getting sick until middle childhood–not until children are older than six or seven.
However, my own research suggests that we can teach kids as young as four some healthy habits if we give them the right kind of information.
We found that four- to seven-year-old children who knew that touching a sick person might make them sick later avoided touching the toys of an experimenter who they thought might have a cold.
Even the youngest children who happened to know that interacting with a sick person could make them sick avoided contact with a potentially sick experimenter. The implication here is that even children as young as four and five are capable of learning how illnesses spread; most of them just haven’t yet.
Tips for parents
Children do not learn much if you just teach them a list of dos and don’ts, like “wash your hands before you eat,” or “don’t go outside without a hat”.
The key is to explain why something like washing your hands might be useful. In other words, you can tell a child to wash their hands before they eat, but it might not be effective in promoting healthy behaviour unless you tell them that exactly what they are washing off and how it could make them sick.
In the end, talking to children specifically about germs and how germs spread might be the most effective strategy in promoting healthy behaviours, even in preschoolers.