Comparison of My Three Sons' Language Development

I tracked the language development of all three of my sons. I wrote a post focusing on Theo’s language development, another post focusing on Cory’s language development, and a final one focusing on Ash’s language development. In this post I’ll compare them all.

The Data

The data was collected by my wife and I using a Google form on our phones. When we heard a new word we would log it. I then normalized the words (sometimes we would write down grandma and sometimes grandmother for the same word, for example) by hand and took the first occurrence of each word in each language as the date when they learned it.

I discuss data collection in more depth in Theo’s, Cory’s, and Ash’s data sections. You can find the Jupyter notebook used to perform this analysis here (rendered on Github). The data can be found here, here, and here.


Below I have plotted the number of words each of my sons knew as a function of their age. Theo, our first son, is represented by dotted lines; Cory, our second son, is represented by dashed lines; Ash, our third son, is represented with solid lines.

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

Cory learned all of the languages much faster than his brothers. Theo was the slowest to learn English and Chinese, the primary languages of our household, but slightly faster than Ash on Spanish, Sign, and Animal Sounds. Interestingly, Ash’s Chinese started strong but has slowed; had we kept recording I suspect Theo would have caught up and passed him at 26 months of age.

I discuss the slow Chinese acquisition in the development section of Ash’s post, but briefly I think it is related to me working from home during the COVID pandemic. This meant that:

With one additional month of living with Ash (not reflected in the chart and data) his Chinese has really taken off recently, using whole sentences instead of just a few words, which leads me to suspect that the slowdown in the data is mostly due to the selection effect mentioned above.

Also interestingly my wife tells me that Cory’s current Chinese is worse than Theo’s was at the same age. Perhaps Cory’s development slowed or there is more to proficiency than just number of words known.

The shape of the English curves are all very similar, just displaced in time. I would guess this has to do with the fact that they are always surrounded by English speakers to learn from whereas the other languages require special interactions with their family to learn.

Ash’s Spanish has taken off much slower than our other two sons, although in comparison he is not too far behind Theo. Theo’s long drought of Spanish words is due to an injury my mom sustained that prevented her and my father from watching Theo and so reduced his contact with Spanish. Ash doesn’t have the same excuse, but it does show it’s not too late for him to pick it up.

Ash never got much into sign language. He learned pointing quickly and got by just doing that until he could speak. We also didn’t emphasize it as much because we were very busy with our other two boys. I suspect this is why he didn’t know as many animal sounds as well: I used to sit with Theo and Cory and point at animals in books and teach them but I did not do this with Ash.

As a final note: our kids’ doctors were worried about both Theo and Ash’s language development being too slow. Some of that worry transfered to us as parents. Keeping track of their words like this was reassuring—we could see that Ash was on pace compared to Theo, and we knew Theo turned out fine!

Other Writings on Language Development

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

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!
My Son's Language Development
My son is a little over two and unfortunately he has two huge nerds for parents. We tracked every word he's spoken to watch his language development, and now you can join us!