I'm a pediatrician. Every parent should know these 'secret' developmental milestones

Crawling, the first word, the first steps — these are just a few of the key milestones in early childhood development that parents eagerly await as their child grows up.

However, there are other milestones or completely normal behaviors which may be not in the traditional checklists, guides and parenting books. Some of these may actually seem concerning at first for parents, even if they are also indicators of development.

Recently, a pediatrician went viral on TikTok for sharing some of these "secret" or hidden milestones that parents ask about. Dr. Sami, who runs an account called @thepedipals, posted the video on TikTok, which now has over 1.8 million views.

"A lot of times parents will ask me, is this behavior normal? Why is my child doing this? And they're concerned. ... It dawned on me that the reason was because it's not really listed as a milestone online or in books," Dr. Sami tells TODAY.com.

Sami says her intent behind posting the video was to go through some of the most common "secret" milestones to help ease parent's minds and educate about childhood development.

So what are some of these commonly overlooked milestones? We spoke to Dr. Sami and another pediatrician to find out.

While the experts consider these to be normal milestones, they acknowledge every child is different. If you're ever concerned about their child’s development or health, consult your pediatrician.

"In terms of newborns, hiccups is one of the most common things we get asked about ... in those early visits," Dr. Anjuli Gans, an attending pediatrician at the Children's Hospital of Philadelphia, tells TODAY.com. Frequent hiccuping is very normal, she adds.

Hiccups are involuntary spasms or sudden movements of the diaphragm muscle, which controls breathing, per the Mayo Clinic.

In newborns and infants, their diaphragm muscles are getting much stronger, says Gans, and the part of the brain which controls these reflexes is also developing very quickly. Their gut is also changing, says Gans, so they may become gassy suddenly.

Hiccups are also caused by irritation of the phrenic nerve, says Sami, which controls the diaphragm. "A lot of the times because babies are starting to eat and drink and starting to expand their stomachs, it can (irritate the nerve) and make them hiccup a lot," says Sami.

“The hair pulling is actually just an expression of them being able to grasp objects,” says Sami, adding that this is very normal even if it’s a pain. Despite their size, babies can pull with a lot of force.

“Around four months, infants suddenly get this incredible strength, and that’s when they start grabbing your face or hair incredibly hard, so hard that you want to cry,” says Gans.

Babies will often master grasping onto things before they meet the the milestone of being able to let go, says Sami. “They’ll just grab for dear life, and the next thing you know you’re trying to unclench their little hands and get your hair out,” Sami adds.

It’s no reason to worry, the experts note, but a good reason for parents and caretakers to start tying up their hair to keep it out of reach from tiny grasping hands.

It's common for newborns to "scream bloody murder," says Sami. Because they only have one type of cry, an alarming shriek can mean anything from hunger to tiredness — but it can be very distressing for parents, says Sami.

"Often newborns cry without anything being wrong, but they cry in such a way that they make it seem like it's an emergency," says Sami, adding that this is an "instinctive cry," and it's normal.

Around four to five months, children will start to develop different cries for different reasons, says Sami, which can help parents understand what they want or need.

However, around six to nine months, babies become more vocal and realize their crying can get a response from people, says Gans. The result? Ear-shattering, high-pitched screeches for no reason.

"They often shriek at the top of their lungs incredibly loudly and sound like pterodactyls," says Gans, adding that this can draw unwanted attention in public and be very frustrating for parents. However, it's a normal milestone and part of a child's vocal and language development, the experts note.

A common milestone you don't always see listed is when a baby stops pooping overnight, says Gans, which usually happens around four months. "Their gut develops in such a way that their stools kind of stabilize," says Gans, adding that they may still urinate and wake up with a wet diaper.

This can be a big deal, says Gans, because it can mean more sleep (for everyone). Occasional overnight pooping may still happen from time to time, and some children may take longer to reach this milestone than others, but that's normal, as well, the experts note.

Potty training in general is a very variable experience. "It can feel like this kind of rat race for parents," says Gans, adding that most children aren't ready to potty train until about 2, and many will follow their own trajectory.

"The reality is that most kids aren't even fully dry overnight until they're at least 5 years old," says Gans.

Another common milestone for infants is when they start shaking or trembling their heads and body, says Gans, which typically begins in the newborn stage and can continue to 4 months old.

"A lot of parents will say they look like little zombies, and the second you touch them ... sometimes they shake a lot and it can be really concerning," says Gans, adding that this shaking or trembling is often totally normal as the baby is developing their reflexes.

Newborn babies have something called a Moro reflex, says Gans, which can cause them to move or shake abruptly in response to different stimuli or triggers. It usually disappears after about two months.

“Somewhere in the six to nine month range, babies may also start shaking their head a lot, and it’s just because they’re discovering their different body parts and how to move them," says Sami.

Unfortunately for parents, temper tantrums are a very normal part of childhood development — but this milestone may come earlier than parents expect, the experts say. You often hear about the "terrible twos," says Sami, but tantrums can begin much sooner (as early as 12 months). This isn't something to worry about, though.

"As soon as the baby has a need and (when) they're not able to communicate through words, they are able to throw tantrums and express frustration," says Sami.

Tantrums can also continue well into preschool, says Gans. Experts and parents have coined a new term, she adds: threenagers. This is used to describe the very emotional, stubborn and awkward phase when a child is transitioning from being a toddler to a young child. "There's a lot of change, and a lot of separation anxiety that can happen during the day and also in the night," says Gans.

While distressing for parents, it's fairly normal for children to become risk-taking daredevils once they can walk and climb around, the experts note.

"Around 15 to 18 months, they start to do very dangerous things, and they don't have any concept of what's dangerous or not," says Sami. Children may climb out of their highchair, do trust falls off the couch, or jump into swimming pools with no fear.

“They feel like they can do a ton more than their little bodies can actually do just yet, and they’ll try anything,” says Gans, adding that head bumps become very common around this age.

Often, young children will do these reckless activities and be surprised when they get hurt, and it can take some time for a child to understand risks and consequences. “It’s a very tiring phase of parenting,” says Sami.

Lying is actually a normal milestone in a child’s cognitive development, the experts note.

When children reach kindergarten, around 4 to 6 years old, Gans says it’s common for them to start telling lots of lies. They may come up with elaborate, unbelievable tales about themselves, friends or school — blending imagination with reality.

This type of lying during this age is often not a serious problem, according to the American Academy of Child and Adolescent Psychiatry. “They’re just having a lot of fun,” says Gans.

During this time, the pre-frontal context of the brain — which regulates our thoughts, emotions and decisions — is developing rapidly, says Gans. A child’s lies often start out as benign or cute, she adds. But as children get older, they may learn to lie to get away with certain behaviors, avoid consequences or get attention.

Picky eating is normal and common, says Sami, and most kids reach this milestone between the ages of 2 and 4.

“After the age of 2, children grow a lot less fast, and so because their rate of growth slows down, their caloric requirement goes down a lot,” says Sami — so it’s normal for children around this age to not want to eat very much or care about eating.

“A child might just be snacking all day, and that’s enough calories to sustain their growth,” Sami says.

Children at this age are also learning to say no and communicate their preferences, so it’s normal to see this happen around food. “They don’t have that maturity to know what a well-balanced diet is, they just want what they want,” says Sami, adding that some children are pickier than others.

Many children will grow out of it at some point, says Sami, but it often happens slowly. “Parents should know that it’s a marathon, not a sprint,” says Sami.