My son was about four months old when I first noticed that he liked to spend a long time doing the same thing over and over again.

Most of his waking hours, when he wasn't eating or pooping, he focused on trying to touch the toys in the mobile over his crib. And he kept at it for weeks, even after he'd mastered the work of touching and tugging at the toy.

Now my son is 3 years old and still busy doing things on repeat — everything from eating his favorite foods, to playing with certain preferred toys, to watching the same YouTube videos again and again.

There was a period of time last summer when all he wanted to watch was a video about tractors and farm equipment. He watched it so often that I became allergic to the soundtrack — my brain would start to shut down every time I heard the dull, mildly melodic background music — but the little guy's enthusiasm for the video was unwavering.

As annoying as these repeated tasks might be to us parents, repetition "has many functions" in childhood development, says Rebecca Parlakian, senior director of programs at the nonprofit Zero To Three, which focuses on early childhood development.

One of those functions is learning and mastery.

"Small children are truly the most persistent humans," says Parlakian. "They are just driven to master the world around them. And they do that through repetition."

And there's a neurological basis to this, she adds. Learning requires building neural circuits, and repetition enables that.

"Brain wiring is made possible by repetition," says Harvard neuroscientist Charles Nelson, III. "If you have a whole group of neurons that have to start to develop into a circuit, they need to be fired over and over. Neurons that fire together, wire together."

From the late prenatal weeks through the first few years of a child's life, the brain overproduces synapses – the connections between neurons, explains Nelson.

"What's special about those first few years, it's taking advantage of this immense plasticity because of this overabundance of synapses," he says.

That plasticity allows children to learn and develop new skills, and therefore neural pathways. As new neural circuitries get established with experience and repetition, the excess, unused synapses are lost, or pruned.

"When you say sounds over again ... what you're doing is consolidating a circuit and pruning away exuberant synapses," says Nelson.

And over the course of childhood and even adolescence, that sets up the entire circuitry of the brain, with each region and circuit specializing in their various roles. .

"We have this phrase in our culture – practice makes perfect, but when it comes to brain development, practice makes permanent," says Parlakian.

Toddlers and children are like little scientists, she says. They are always testing and retesting to figure out the rules of the world around them, and they do this through repetition.

"Think about a really common scenario, like a child, a baby even, throwing food off the highchair, and the dog, you know, leaps on it and eats it up," says Parlakian. "And it's this wonderful, satisfying game until the baby runs out of cheese and then throws the spoon off the side."

And that's how the baby learns that the spoon scares the dog away.

"All of a sudden the game has changed and they really learn something about how their world works."

As children learn things by doing things over and over, she says, they also start to take some comfort from being able to predict how something will unfold.

"There's something so nurturing when you can anticipate exactly what will happen in a routine or in a story."

That's especially obvious during our son's nighttime routine, which involves my husband or I reading his favorite books, sometimes days or weeks of the same book (often involving construction vehicles) over and over again.

Now I understand that this nightly routine has already taught him so much about different types of trucks, their individual roles and how they help create the urban environment we inhabit. And it has also brought him the comfort and safety of knowing that once we're done reading, he will fall asleep with his head resting on my shoulder.

So, if you're a parent of a little one feeling exasperated at your child's repeating loops of jokes, or games or stories, know that they are just hard at work practicing and mastering their newfound knowledge and skills, and building the architecture of their brains in the process.