Unfortunately, there's no way to prevent someone from suing you. You can be sued, even if you didn't do anything wrong. For example, reasonable minds could differ as to whether you were negligent in your supervision of the children.

Even if you had some form of waiver, it could not, from a legal standpoint, be so comprehensive that no one would ever have the ability to sue you. Your business model involves a number of lightning rods: it's in your home, and you're dealing with children. You may well have licensing, zoning, and child-care certification-related legal issues as well.

Homeowner's insurance may not cover your business-related activities. If you can't afford insurance at this time, you may want to go back and crunch the numbers to get a clear handle on your start-up costs and timing. If you'd really rather be safe than sorry, you may want to wait until you have the funds available to invest in the right insurance and professional services that can offer you some protection.