The children of Aaron - i. e., the priests.

And David assembled the children of Aaron, and the Levites. Whose business it was to bear the ark when there was any occasion for it: and from hence to the end of 1-Chronicles 15:10 an account is given of the Levites, and their number employed in this affair:
of the sons of Kohath; a son of Levi, that is, of his posterity; for his immediate sons, and so those of the rest after mentioned, had been dead ages ago; the principal of those, at this present time, was Uriel, and his kindred, or those of the same family with him, were one hundred and twenty: of those of Merari, another son of Levi, the chief was Asaiah, with two hundred and twenty of his relations: of those of Gershon, another son of Levi, was Joel, and his brethren were one hundred and thirty: of the posterity of Elizaphan, a grandson of Kohath, Exodus 5:18, the most noted was Shemaiah, who had two hundred of his family with him: and of those of Hebron, the son of Kohath, Exodus 6:18, Eliel was the most famous, and he had eighty of his kindred with him: and of those of Uzziel, another son of Kohath in a different line from Elizaphan, who also was a son of Uzziel, was Amminadab the chief, who had one hundred and twelve of his kindred with him: the number of Levites, in all, gathered together, were eight hundred and sixty two, besides their chiefs.

David assembled the children of Aaron, and the Levites--The children of Aaron were the two priests (1-Chronicles 15:11), Zadok and Abiathar, heads of the two priestly houses of Eleazar and Ithamar, and colleagues in the high priesthood (2-Samuel 20:25). The Levites were the chiefs of their father's house (1-Chronicles 15:12); four belonging to the Kohathite branch, on whose shoulders the ark was to be borne; namely, Uriel, Shemaiah--descended from Elizaphan or Elzaphan-- (Exodus 6:22), Hebron (Exodus 6:18; 1-Chronicles 6:2), and Amminadab from Uzziel (Exodus 6:22).

From among assembled Israel David then specially gathered together the heads of the priests and Levites, to determine upon the details of this solemn procession. "The sons of Aaron" are the high priests Zadok and Abiathar, 1-Chronicles 15:11; and the "Levites" are the six princes named in 1-Chronicles 15:5-10, with their brethren, viz., (1-Chronicles 15:5-7) the three heads of the families into which the tribe of Levi was divided, and which corresponded to the three sons of Levi, Gershon, Kohath, and Merari, respectively (Exodus 6:16): Uriel head of the Kohathites, Asaiah of the Merarites, and Joel head of the Gershonites, with their brethren. Kohath is first enumerated, because Aaron the chief of the priests was descended from Kohath, and because to the Kohathites there fell, on account of their nearer relationship to the priests, the duty of serving in that which is most holy, the bearing of the holiest vessels of the tabernacle. See Numbers 4:4, Numbers 4:15; Numbers 7:9; as to Uriel, see on Numbers 6:24; for Asaiah, see 6:30; and as to Joel, see 1-Chronicles 6:33. Then in 1-Chronicles 15:8, 1-Chronicles 15:9 we have the heads of three other Kohathite families: Shemaiah, chief of the sons of Elizaphan, i.e., Elizaphan son of the Kohathite Uzziel (Exodus 6:22); Eliel, chief of the sons of Hebron the Kohathite (Exodus 6:18); and Amminadab, chief of the sons of Uzziel. The sons of Uzziel, consequently, were divided into two fathers'-houses: the one founded by Uzziel's son Elizaphan, and named after him (1-Chronicles 15:8); the other founded by his other sons, and called by his name. Of the fathers'-houses here enumerated, four belong to Kohath, and one each to Merari and Gershon; and the Kohathites were called to take part in the solemn act in greater numbers than the Merarites and Gershonites, since the transport of the ark was the Kohathites' special duty.