Another example:
The grammatical gender is transparent is Spanish. “a” indicates a feminine gender. “o” indicates a masculine gender. The Spanish children have learned this principle by the time they are 2 years old.
In Welsh, the grammatical gender is more complex. The Welsh speaking children master this principle when they are much older, around 10 years old.
Principle 5:
Exposure to the language for timing/speed of development.
There is a critical mass of input data to the acquisition of the language. The more the child is exposed to the language the faster the child can reach the critical mass of knowledge.
BUT the exposure with complexity and cognitively is more relevant.
The exposure to the languages can delay initially the development of the bilingual structures. The child needs more time to get to the critical mass.
The emergence of the structure of the language comes from the accumulated knowledge.
Monolinguals and bilinguals learn the simple forms first and the more complex forms of the language later.
The child has the innate abilities to learn the first 3 principles. The 5th principle is only under the influence of the input of the learned language, i.e. it is up to the parents/environment for the child to learn the language.