Paulina Rubio -- My Ex Wants to Use Our Kid to Attract Paparazzi

Paulina Rubio and her ex-husband are in an international tug of war over their kid -- she's accusing him of lying about plans to take their son out of the country ... while he claims she's blocking him from seeing the child.

We broke the story ... Rubio and Nicolas Vallejo-Najera have been battling over their 3-year-old son, Andrea ... accusing each other of violating the timeshare agreement.

In new court docs, Vallejo-Najera claims he hasn't been allowed to see Andrea for weeks -- forcing him to file an emergency motion late last month demanding Paulina hand over the kid ... so he can fly to Spain.

In her own docs, Rubio accuses her ex of constantly changing travel dates -- and she claims the real motive for the trip was merely to use their son in a set-up photo shoot with paparazzi.

A judge will decide whether the kid stays or goes.