Angel(s) - Explanation 

Jesus Christ is not the Image of word alone, but the Image of invisible trinity God, that means in Jesus Christ we can see our Heavenly Father (I and the Father are one - John 10:30), and the Son (He who came down from heaven, that is, the Son of Man who is in heaven - John 3:13), and the Holy Spirit (if I do not go away, the Helper will not come to you - John 16:7).

Who are these that Jesus Christ referring as "Their Angels"? - See that you do not despise one of these little ones. For I tell you that in heaven their angels always see the face of my Father who is in heaven - Matthew 18:10

And Lord gave one clue about these Angels that "They always see the face of the Father who is in heaven", and that clue directly pointing to Jesus Christ because - No one has seen God at any time. The only begotten Son, who is in the bosom of the Father, He has declared Him - John 1:18

Then why Jesus said as "Their Angels" in plural, Because Jesus Christ is our Heavenly Father, Son(Word), and the Holy Spirit - and there are three who are testifying in the earth: the Spirit(Holy Spirit), and the water(Father), and the blood(Son) and the three are into the one(Jesus Christ) - 1 John 5:8