Carrie Underwood's kids may be joining mom in the biz! Underwood spoke to ET's Rachel Smith backstage at CMA Fest in Nashville Sunday, where she revealed that her sons have a flair for performing.Underwood's sons, Isaiah, 7 and Jacob, 3 — who she shares with her husband, Mike Fisher — were caught on camera in a now-viral video after they crashed the stage during their mom's performance at the Grand Ole Opry. The «Ghost Story» singer told ET she had no idea they were dancing behind her — at first.«That was called, it's way past my bedtime,» Underwood joked.