Quoting They call me mama.:" Children often are scared of eating much after having a stomach bug. I couldn't get my daughter to eat ... [snip!] ... less energy so that could explain the sluggishness. The stomach flu can be a bit traumatizing especially for young children."
This! About a year ago DD had a pretty bad stomach bug and i couldn't get her to eat at all, finally one day my mom got me this turkey, cheese and crackers platter and DD said she wanted some. She ate almost the whole thing and that's all she ate for a few days before she felt comfortable enough to eat other things.