The major theme of sefer Vayikra is, arguably, that of tumah and taharah, purity and impurity. When one reads the Torah, one senses what seems almost an obsession with this topic. If one happens to violate the special sanctity of the Temple, or of sacrifices, or even of the camp of Israel, the penalties are severe and harsh.
Modern psychological research has shown that infants begin processing information even before they are born, and impressions made on children have an everlasting effect. It is for this reason that the Mishna in Pirkei Avot (2:11) heaps praise upon the mother of Rav Yehoshua for bringing him to shul as an infant. The Torah itself commands that little children, and even infants, be brought to Jerusalem on certain special occasions; the atmosphere of holiness experienced by these children would stay with them forever.