Are there any grants out there for someone that wants to develop a camp for obese children?

These types of camps already exist so I don't know that there's much money available to create more. Perhaps you should volunteer at one or more of these to see if this is something you really want to get involved in first, then look into the financial aspects. You also need to do some market research to see if there's a need for another weight loss camp. In addition, obese children may not have an interest in hiking and may not have the stamina to hike. Most horses don't carry people over 200 pounds - will you ban the very obese kids from riding horses? What will you do with surly kids whose families have forced them to go? How will the families pay? Will you accept health insurance coverage? Will health insurance companies even want to be involved in a new venture? Do you have a business plan? Do you have mountains of money to pay for the insurance on this type of thing? Will you township even allow you to do this?

I think you need to do some more research to see if you idea is really practical.