Justin Bieber really loves his little brother Jaxon and little sister Jazmyn! It was Jaxon's 4th birthday (Nov. 20) and The Biebs lead the serenade of 'Happy Birthday' and helped the little one blow out the candle on his cake.

Poor Jaxon started crying when their dad Jeremy Bieber smashed his face into the cake while they were posing for a picture! Poor kid.

"He did it to me, too," The Biebs said about his dad, trying to comfort his little brother, who was beyond pissed that he got cake on his face.

Jax got over it quick and later smashed his own face in the cake.

What a cutie pie, er, cake.

The party took place at the shoot for The Biebs' video for 'All That Matters.'

Jaxon had a star-studded party, as Floyd Mayweather was said to be in attendance, too. Plus, he has Justin Bieber serenading him on his big day. What a life.