Not too hard. It's just each letter replaced with another one. If you got a text coded like this you can just start making guesses. For example if you see one word with three letters like "CQX" repeatedly in a text of code, you can guess it's either a "the" or "and" Then you just go and test what happens when you replace every C in the Text with a T because you guessed CQX could be THE and also every Q with a H and every X with an E... Then you look for words that have those letters and only one more letter missing so you could guess the whole word. Like here for example CQXY you already replaced CQX with THE, so you could guess Y could be a M or N so it's a THEM or THEN. Then you go and replace every Y in the text with a N or M and look which one makes more sense. Just go on like this and you can figure out every letter and thus the whole text. This is what OP allegedly did here. (If he didn't create all this on his own)

Here are all letters and their counterparts for this code:

A=C

B=Z

C=T

D=I

E=N

F=W

G=V

I=P

J=K

K=G

L=Y

M=R

N=X

O=F

Q=H

R=B

S=A

T=D

U=L

V=S

W=O

X=E

Y=M

Z=U

H=J or Q P= J or Q

Try to find other comments on those "kids videos" using this code to verify, that it isn't a hoax by OP. I couldn't find any yet. Probably fake, but let's give it a chance.