It is common to speak of the surprising "hatching" of language in children because it is not understood how this faculty, which has not been an evolutionary necessity in Homo, can appear so early (2 and 3 years). The last widely discussed hypothesis, influenced by the genetic discoveries of the last century, has not been satisfactory either. In the preceding document "Knowledge of children at 2 years of age", the appearance of the first cognitive processes is explained: the simplest-sensitive concepts (cat, "bug", ...), which are made possible by a "recycling" of the child's psychomotor faculties which are transferred to language (so little to do with genetics). And at the age of three, in his attempt to copy the language of adults, the previous conceptualisation together with the identifiers of his environment (his relatives, his cat "Mischa", ...) allow the faculty of intuitively managing the "Terminations" (Endings) of words to appear, by recognising without error their complex phenomenological correspondence. The explanation of this surprising faculty was advanced by FREUD in a document of 1895 but which was not discovered until 1950 (the so-called "Psychology Project"), in which he also advanced the concept of synapses (synapses discovered by LÖWI in 1921), and even FREUD described them more correctly than in the later neurological conception, which is confirmed by the most recent contribution of LLINÁS, since LLINAS he also revealed the error of the prevailing hypotheses until then about their functioning, which is not to be found in the chemistry of their neurotransmitters. The "Knowledge of children at 3 years of age" completes this unfinished "Project...", showing the total correctness of his intuitions, as well as the human impossibility that 125 years ago he could have progressed beyond what he had already contributed. Thus, he adds how synapses work, which is explained by the informational unconsciousness dynamics of the psyche, through the nervous system (the simile of the "Tele-tac" of the toll highways), already intuited by FREUD. In turn, the emergence of the child's neuronal interconnections and their minority genetic and physiological causes, highlight the informational importance of the stimulus, and consequently the need for an "aRb" relational model of the human psyche, as well as the unfeasibility of the perspectives and hypotheses currently in force. It also implies a linking of neurology and psychology, as well as the future line for the progression of both, in parallel and without interference as hitherto. In the expression of a well-known chemist, it is the third strand to be added to FREUD and RAMON y CAJAL in order to achieve a "scientific psychology". This series of papers (which will continue with knowledge at 6 and 10 years) is an adaptation of the 1996 writings on the "Representation of knowledge", i.e. what are the processes that make human knowledge possible, a representation validated by its correct computer simulation and which in turn solved the challenge of LEIBNIZ's "Characteristica universalis". Since, in spite of this validation, it was not possible to make it understood due to its many innovations, -it represents a radical change of scientific paradigm, with its usual initial rejection-, this series has been rewritten in a way closer to current knowledge in order to make it more comprehensible, which in turn has made it possible to explain various pending problems of language and psychology, in addition to the neurological ones already mentioned. It is therefore inevitably long, with many collateral explanations and several annexes, since it has had to clarify the many misunderstandings of current science, which is still restricted to its exclusively material perspectives, without having yet incorporated information into its most basic paradigms. Annex 2 of 13 March 2021 cites an article by other researchers (DEISSEROTH, ...) that confirms the certainty of this document. And Annex 3 of 17 July 2024 cites another (YANG, BUZSÁKI, ...) with new further confirmation.