Erika Goldring/Getty Dave Grohl took a break from headlining festival ... old son Shane for a special set with Hawkins’ former side-project Chevy Metal at Simi Valley’s Rock & Roll Pizza ...

The alleged mother of Dave Grohl's secret ... child's face was not in view, but the kid wore a red beanie and matching booties. As for Dave's location, he was not spotted at her side.