Diddy's Sons Justin and Christian Post Father's Day Messages to Him

6:03 PM PT -- Diddy's daughter Love also sent her pops a Father's Day greeting ... or at least whoever runs her social media did. It's a pic of Diddy holding Love -- who turns three later this year -- with the caption "Happy Dada Day! 💕🥰."

Diddy might be spending Father's Day behind bars at MDC Brooklyn ... but, his kids are still sending him their best -- sharing loving posts amid his federal trial.

Justin Combs posted for his dad late Sunday afternoon ... sharing what looks like a behind-the-scenes video of Combs at a group meeting -- with Diddy telling the camera it's a proud day for him.

Diddy seems to be speaking to Justin, Christian Combs and Quincy Brown -- Kim Porter's son who he adopted -- who are listening intently to their dad.

The video ends with the whole group getting hype ... lots of screaming and hugging -- overall a sweet moment between a father and his sons.

Christian also posted for his dad ... sharing a pic where he's very young on the red carpet with Diddy -- arms wrapped around his dad.

He captioned that post, "Happy Fathers Day Pops!! I Love you & miss you !!! We waiting for you at 🏡." At the time of publishing, his twin daughters -- D'Lila and Jessie have not posted for him.

Diddy's trial is rolling on in New York City ... with the 24th day of testimony set to begin tomorrow as he fights off sex trafficking and other federal charges.

The trial's been full of twists and turns -- both in the courtroom and in the overflow galleries where Kanye West made an appearance last week -- and, the verdict is still very much up in the air at this point.