Research shows that up to 70% of typically developing kids engage in repetitive and seemingly purposeless movements like leg shaking, nail-biting, or hair twirling. And not only are these quirks typical, but kids have them for a reason: They're a way to self-regulate their senses. "Once you understand what your child is doing why they're doing and the purpose it serves, you'll no longer look at it as a quirky habit but as behaviour with a purpose," says Amanda Bennett, M.D., a developmental pediatrician. Here are four of the most common quirks.

Sucking on things

"Kids who gravitate toward mouthing, chewing, and sucking may be doing so because their mouth is somewhat undersensitive," says Biel. In other words, your shirt sucker may have decreased oral sensory sensitivity and require more in-the-mouth input to satisfy that need. "For these kids, it's likely that this mouthing behaviour releases feel-good, soothing neurotransmitters like serotonin and dopamine, which help them feel calm, less bored, and more engaged," explains Biel.

Mouthers are often the same kids who drooled past babyhood, experienced a speech delay, or are messy eaters, says Biel. "They often have trouble mastering precise movements of their lips and mouth because they simply don't process those tactile sensations as well as other children."

While these behaviors are generally harmless, you'll want to brainstorm and redirect if your child's chewie du jour is a germ fest, a choking hazard, or otherwise harmful. For instance, if thumb or finger sucking continues beyond age 2-4, it can affect the shape of a child's mouth or cause an ortho issue like an overbite, according to the American Academy of Pediatrics.

Rocking and spinning

While a kiddo who rocks themselves to sleep may seem worlds apart from one who spins in circles after a long day of school, they're not. Both are working hard to jostle the fluid, the hairs, and the tiny calcium-carbonate crystals in their inner ears that make up the vestibular system, which monitors motion and balance.

Kids who naturally rock, spin, swing, or bounce likely have a vestibular system that requires more movement than most because they have a lower-than-average sensitivity to the stimuli. The key with these quirks? Knowing when enough is enough. There's something called an inverted U-curve. When a child spins, their arousal goes up and their ability to stay calm and focused improves. That is, until they get to the top of the curve, when arousal continues to go up but performance goes down.

Going overboard can bring on both, immediate and delayed sensory-overload issues. It's important to work with your child, and possibly an occupational therapist, to pinpoint the top of the curve. For instance, you may want to limit your spinner to one revolution a second for no more than 10 revolutions and then switch directions. "Stopping and restarting benefits kids by giving the most information to their vestibular receptors, which process movement information," says Biel. It's also smart to have special toys at home that fulfill your child's sensory needs.

Sniffing things

"Smell is the one sensory system that connects directly with the limbic system, which is the emotion, memory, and pleasure center of the brain," says Biel. "It's all about association, and kids often sniff things that conjure up pleasant memories that they find comforting." These soothing smells can simply help a child feel more safe and secure – or relaxed enough to facilitate sleep.

Fidgeting

Touching, feeling, squeezing, poking, hair twirling, and all other similar forms of fidgeting generate sensations that feed a child's hunger for touch. The body releases the feel-good neurotransmitter oxytocin in response to finger and hand tactile-seeking movements, like repeatedly touching a soft tag or gently stroking your hair, according to research.

Beyond the calming effect, fidgeting can help kids concentrate too. We know that all children move more during challenging mental activities than they do during ones that are less challenging. Children are using small movements to stimulate their brain. For some kids, particularly those with ADHD, the fidgeting helps keep their brain engaged and bolsters working memory.

However, the once-popular fidget spinner has actually been found to do the opposite. When kids use fidget spinners in the classroom, they're actually more distracted. It's important to find a way to fidget that actually works for your child – without disrupting class. For example, if your kid is a serial arm squeezer, you could make them a homemade squeeze balloon filled with baking soda that they can squeeze every time they need to squeeze.

When a Quirk Is a Bigger Deal

If your child's behaviour interferes with their everyday functioning – say, they're so bothered by noise that they hate recess or won't ride the school bus – it could be a sign of a sensory processing disorder, says Sara O'Rourke, an occupational therapist. Kids with the condition can't respond appropriately to the signals coming from their senses, while those with typical quirks have found a way to self-regulate. If you're concerned, talk to your child's pediatrician, who can refer you to an occupational therapist for strategies.