According to this from the BBC News website if your child is born by Normal Vagina Delivery there less likely to become fat. Problem is that a risk factor for needing a C section is a big baby, diabetic mother etc, which are also risk factors for having an obese child.
The only true way to find out if having a C section would be a risk of causing obesity in itself would be to conduct a randomised controlled trial. Get one thousand pregnant women and randomly allocate them to NVD or to C section. Then follow up the kids in ten years time and see if they are fat or not.