Nick Cannon Celebrates 2-Year-Old Twins' Birthday Before Father's Day

Nick Cannon had a busy Father's Day weekend, which kicked off with him celebrating the birthday of his second pair of twins ... and ended with seeing some of his other children too.

Every year, folks wanna know what Nick's up to mid-June ... and every year, he rises to the occasion -- making pit stops all over town like Santa Claus on Christmas Eve. This year proved no different, Saturday was dedicated to his toddler twins Zion and Zillion ... whom he shares with Abby De La Rosa, and who turned 2 before the holiday.

BTW ... their third baby together, Beautiful, was living it up next to her older siblings too.

Seeing how it was their special day, Nick hung out with them and their mom at Sesame Place in San Diego ... and the photos of them at the park are awesome!

Nick documented the trip on social media -- with a great highlight video showing off their visit -- but eyewitnesses tell us it was even more special behind the scenes ... with a whole crew of friends and family tagging along, all of whom enjoyed SP's many attractions.

For example ... we're told Nick and co. took everything in -- from the daily parade to the Sesame Street stage show, as well as the wave pool and Elmo's Silly Sand Slides.

There were also meet-and-greets carried out for his kids with Sesame Street characters, and carousel rides too. In other words, the parents went all out for Zillion and Zion here.

Nick was clearly stoked about ringing in the twins' birthday alongside Father's Day in a little two-for-one bash. He took to social media and wrote, "My little guys turned the BIG 2 this week! Thanks to our friends and family who came together to help us celebrate Zilly & Zion!

Now, as for Sunday itself -- the almighty Dad Day -- it appears Nick split his time with a handful of his other kids. And, like he's done before, NC made the rounds for some face time.

From what we can see on his social media ... Nick went to visit -- or at the very least, received gifts -- from four other children of his, and they were all giving it up for Papa Bear in their own unique way.

Remember, Nick's got 12 children total ... it's unclear if he went to see each and every one of them. In any case, he was certainly on a kid sprint -- only lord knows how he does it all.