Otto explains that borrowing occurs when the concept a person wishes to use is not available in the second language. But this process is different depending on the stage at which the vocabulary is learned. Children who have acquired two languages ​​before the age of three will develop both vocabularies at the same time. On the other hand, in children over three years old, the acquisition of second language vocabulary will be diminished during the preschool years, mainly because it is limited to practice at certain times of a day or a week. It should be noted that although "code-mixing" and "code-switching" can occur, children develop independence from one language to another more quickly than adults.