I ask for copies of their imunization record, but not birth certificates or health cards. Playfelt had some great advice in terms of thinking about what you are looking for a child to have before starting with you. I personally, have no problem starting them younger as they often adjust so much more easily and quickly and I have had kids start with me at 1 year of age who could not walk until they were 18 months, so being one doesn't guarantee anything really.