First we observe, that a person is not born a Karaite Jew even if both his/her parents are native born Karaite Jews. Such children are born Jewish but Karaite Judaism is not a social club nor can it be genetically transmitted, rather it requires an affirmative act on the part of the individual to pledge to follow the biblical precepts of Tora handed down to us from Abraham, Isaac, and Jacob and of course Moshe, our Teacher and the prophets and holy writings that follow, collectively referred to as the TaNaKh. Thus a child born of Karaite Jewish parents who elects to follow any other variant of Judaism and who rejects setting the calendar by observing the Aviv and the New Moon cannot be a Karaite Jew despite the fact that his parents are Karaite Jews.
The process of transmission of Jewish values to children is one of education in the broadest sense, so that what is transmitted is not merely knowledge but beliefs and values attitudes and ideals, and above all, a sense of identification and commitment The responsibility for transmitting Judaism derives from Har Sinai when our ancestors on behalf of themselves and their descendants pledged their commitment to a covenant with God saying "We will do and hear." (Exodus 24:7)
The transmission of Judaism is a task for each successive generation of Jews.
While there is nothing wrong with the custom of calling a child to the Torah at the age of 12 or 13, the rabbinic practice of calling that child an adult and severing certain responsibilities towards that child is not in accord with our Torah that bestows adulthood at the age of 20 .
Therefore, it is the parent's obligation to teach their children the ways of the Torah, and when they are twenty years old with the help of our Creator, the child will make the right choices. For very small male children it is advisable to circumcise them immediately to avoid them having to make that decision later in life.
It is the practice of the Moetzet Hakhamim (the Council of Sages) that Minors over the age of 10 and under the age of 18 must sign a statement consenting to their conversion and that minors under the age of 10 will be converted without a formal statement.
 Exd 30:14 Every one that passeth among them that are numbered, from twenty years old and above, shall give an offering unto YHVH.
Lev 27:3 And thy estimation shall be of the male from twenty years old even unto sixty years old, even thy estimation shall be fifty shekels of silver, after the shekel of the sanctuary.
Num 1:3 From twenty years old and upward, all that are able to go forth to war in Israel: thou and Aaron shall number them by their armies.
Num 1:18 And they assembled all the congregation together on the first [day] of the second month, and they declared their pedigrees after their families, by the house of their fathers, according to the number of the names, from twenty years old and upward, by their polls.
Num 1:20 And the children of Reuben, Israel's eldest son, by their generations, after their families, by the house of their fathers, according to the number of the names, by their polls, every male from twenty years old and upward, all that were able to go forth to war;
Num 32:11 Surely none of the men that came up out of Egypt, from twenty years old and upward, shall see the land which I sware unto Abraham, unto Isaac, and unto Jacob; because they have not wholly followed me:
1Ch 27:23 But David took not the number of them from twenty years old and under: because YHVH had said he would increase Israel like to the stars of the heavens.
Ezr 3:8 Now in the second year of their coming unto the house of God at Jerusalem, in the second month, began Zerubbabel the son of Shealtiel, and Jeshua the son of Jozadak, and the remnant of their brethren the priests and the Levites, and all they that were come out of the captivity unto Jerusalem; and appointed the Levites, from twenty years old and upward, to set forward the work of the house of YHVH.