My difficulty in remembering English vocabularies, when I was young

It has been more than 15 years since I started my first English class. I remembered that my English classmate was my eldest sister and another of my older sister. I was the youngest in the English class, I started reading English with the monotone just like I read the text in my language, Khmer.

Today, on the tram, on the way back home from my university; I heard a little kid around 2 years old, he cried and said to his mother "ricaricare subito" in Italian, it means, "charge the battery immediately", because he was playing with his mother phone and accidentally the phone ran out off battery.

What that surprised me from his phrase, is that the word "ricaricare", it is such a long word, of 5 syllables; and how the kid here they could remember to use such a long word like that?

From that moment, it reminded me about my difficulty in remembering the English vocabularies, when I was young. I still remember that I cannot remember the word "interesting" and also "difficult", because they are 4 and 3 syllables long; and it is quite difficult for me to remember it. I always tried to remember another word that having more or less similar meaning to those long words, like using "nice" instead of using "interesting"; and also "hard" instead of "difficult".

I tried to find out why it is that hard for me in remembering such those words! I think that it is because of my mother tongue is a single syllable language, most of the word are compose of only single syllable, how ever we still have some words have more than 2 syllables, but not that much, and mostly are the word borrowing from the ancient Indian languages or the word that created by suffix, prefix or infix. I have read an article about the Khmer language, and it said that the word in Khmer that having the longest syllables is the word "Ampilampaek", it is the name of an insect, and it is composed of 4 syllable.