Parade in Chilapa

Earlier this year when I was in Guerrero, Mexico (see Other Side of the Camera and What I Do), I had the opportunity to watch a boisterous parade stream through the streets of Chilapa. Really great with lots of drums, and costumes, and honking horns, and groups of young school kids in uniforms exhibiting a type of Brownian motion as they moved along under the supervision of their teachers. Any idea from the photo above of what the parade was celebrating? [Hint: I took the picture on May 10, 2013]. [Another hint: Mother's Day was celebrated in Mexico on May 10 of this year].