My Son's Language Development

My son Theo was born in the summer of 2016. My wife and I knew his language development would be interesting, because she and her parents speak Cantonese and my parents speak Spanish (although they did not really pass it on to me). Being huge nerds, we decided to record his progress.

The Data

We collected the data using a Google form. We decided a “word” was a phrase or sign that Theo associated with a specific concept. This meant that when he babbled “mama” or “baba” at 10 months we did not count those because he didn’t have a clear association. We did count some made-up words where he had an association, but these were mostly in sign language where he would invent them to convey his meaning.

We found data collection to be difficult and error prone. Deciding when Theo had a clear association was hard because the best indicator was that he used the word multiple times for the same thing. Sometimes these reuses would be separated by many days, forcing us to try to remember when he first used it.

As Theo got older and much better at language, we ran into new issues. First, he was learning so fast that we had trouble keeping up and remembering if a word had been recorded our not. Second, he became so good at mimicking sounds that he would repeat words back to you several times, but not remember them later.

Still, we think the data is a pretty good representation of his language development. I’ll spend a future post exploring some off the quality issues.

You can find the Jupyter notebook used to perform this analysis here (rendered on Github). The data can be found here.


Theo spoke his first word, in Cantonese, at 14 months. He had been babbling for a long time before that, but without associating the sounds with meaning. He then picked up four signs from baby sign language before speaking his second word a month later. We suspect Theo picked up signing quickly because it was a universal language in our house; Mom would only speak Cantonese and I would only speak English, but we both responded to his signs.

Theo’s language development is plotted below, showing the number of words he could speak in each “language” as a function of how old he was.

A plot showing the number of words my son could speak as a function of age.

Theo continued adding signs and Cantonese words for three months before he spoke a word in English, the language I speak to him. That is when he also started mimicking animal sounds. At 18 months his spoke his first word in Spanish, the language my parents speak to him.

Theo slowly added words, week by week, until right before he turned 2. At 23 months his language acquisition exploded. He started the period knowing 25 Cantonese words. He knew 50 a month later, and almost 100 after two months. Theo is now 26 months old and knows almost 200 words in Cantonese. English exploded also, but a little later. At 25 months he knew about 40 English words, and now he knows over 100 a month and a half later!

His Spanish development took off at around the same time, but quickly plateaued, only to take off again recently. The reason is simple: neither of us speaks it well, but my parents do. The quick rise happened when he was visiting his grandparents regularly, and the plateau is when we stopped visiting for a few months while my parents were out of town. Now that we are visiting them again, he has started picking up more words.

The Words

I plotted a selection of some of Theo’s first words in each language below. Notice that I have switched to a log plot for the y-axis to better show the beginnings of each language.

A plot showing the first words my son could speak as a function of age.

In a future post I’ll explore when Theo learned different groups of words (colors, numbers, foods, etc.), but for now here are some of the fun words Theo learned:

Other Writings on Language Development

If you enjoyed this article, here are all the other articles I wrote about language development!

Comparison of My Three Sons' Language Development
I recorded the words my sons spoke as they learned our various languages and now I compare how each developed! Read on to find out how each son learned.
My Third Son's Language Development
We tracked my third son's language development word by word. Here, in plots, is how he learned to speak. Take a look!
Comparison of My Two Sons' Language Development
Being a nerd dad, I recorded all the words my first two sons spoke as they learned them. Now, I compare their language development rate!
My Second Son's Language Development
My second son is a little over two years old. We tracked every word he's spoken to watch his language development, and now you can observe it too!