Can a capsule endoscopy replace an upper endoscopy &colonoscopy for a 3 year old? Is the same prep required for the capsule endoscopy?

Possibly. If you are at an academic center working with pediatric GI and radiology specialists, this can be a great alternative if you just need to look. If they think biopsies are going to be needed, then won't work. And, unfortunately, you do need pretty much the same cleanout so you can get good images form the camera and be able to see what is really going on. Child also has to be able to swallow camera.