Blac Chyna and Tyga Take King Cairo to Six Flags for 5th Birthday

Blac Chyna and Tyga have apparently made great strides in the co-parenting department, because they presented a united front Saturday as they took their son King Cairo to Six Flags Magic Mountain.

It's the kid's 5th birthday, and this time there weren't dueling parties.  The nanny came along for the ride, and some of King Cairo's friends tagged along as well.

Here's a theory ... Chyna's in a massive war with Rob Kardashian and his family, and it's hard to fight on 2 fronts at the same time so her issues with Rob may have made Tyga look like a picnic.