Jamieson, Fausset and Brown on Daniel 1:4

4. no blemish--A handsome form was connected, in Oriental ideas, with mental power. "Children" means youths of twelve or fourteen years old.

teach ... tongue of ... Chaldeans--their language and literature, the Aramaic-Babylonian. That the heathen lore was not altogether valueless appears from the Egyptian magicians who opposed Moses; the Eastern Magi who sought Jesus, and who may have drawn the tradition as to the "King of the Jews" from Da 9:24, &c., written in the East. As Moses was trained in the learning of the Egyptian sages, so Daniel in that of the Chaldeans, to familiarize his mind with mysterious lore, and so develop his heaven-bestowed gift of understanding in visions (Da 1:4, 5, 17).